Byzantium is Roman Empire. The term “byzantium” is coined by german historian in 16th century to delegitimize late Roman Empire because they were orthodox plus they wanted to legitimize “Holy Roman Empire” as the successors of Rome which they could never succeed.

Western and Eastern Roman Empires were never totally independent states. Roman Empire just got divided into 2 administrative divisions to simplify micromanagement since it was not easy to rule such vast lands from one capital.

Western half of Roman Empire got invaded easily, again there was no “Eastern Roman Empire” but simply Roman Empire lost its western half.

Holy Roman Empire is a joke by itself. It is actually “Confederate Kingdom of Pretty German Princely States” who wanted to claim legacy to Roman Empire but they could not. First of all, east-west schism, papal supremacy is non-roman, pope was simply Bishop of Rome. Pope crowning someone as Roman Emperor is ridiculous. Also even coronation is barbaric by means of Roman Empire. Why ?

1- Coronation is given power from a higher source. Roman Emperors would ascend to throne, not get coronated which would seem as an insult.

2- Roman Empire did not have a “crown”. Ornate headgears were deplorable, they were simply random hats of emperors, power was by emperor, not the crown. Culture of coronation comes from Roman Emperor sending crown to his vassals, it is a diplomatic insult that said that headgear hold the power that emperor could grant to anyone he wanted.

Again, Emperors of Holy Roman Empire were not called Emperor or Roman or Holy by anyone pretty much, hence famous Voltaire quote “neither Holy nor Roman nor an Empire”.

Summary:

Western Roman Empire and Byzantium (Eastern Roman Empire) were both Roman Empire, they were not independent states but two administrative divisions of the same empire, one of these divisions got destroyed early on, leaving the other one and only sovereign of Roman Empire.

Holy Roman Empire was Confederate Kingdom of German Princely States with elective monarchy where Habsburg dynasty of Austria bribed electors all the time.

Constantinople's strategic location was probably the single biggest reason the Byzantine (aka Roman) Empire didn’t fall hundreds of years before it did. It really is a brilliant site and one of the most defensible locations anywhere in the Mediterranean basin.

Check out the map.

It is a peninsula, which of course means it is surrounded by water on three sides. The body of water on the north is called the Golden Horn. During the Byzantine period, there was a chain that was stretched across, which you can see as a line in the map. That chain radically limited access from the north.

By land, you had only one wall you had to build and fortify. The Walls of Constantinople (aka the Theodosian Walls) were probably the best built and defended walls in antiquity. They were three layers deep, with a moat in the front.

Assuming you got through that, there was another wall further in called the Constantinian Wall, also seen on the map.

All the area around the shore had a sea wall, which meant that any sea born invasion would have to go over walls as well.

You can also see some topology lines on the map, which shows that the area near the tip was higher in elevation, which gave the defenders a great vantage point.

But this is just the layout of the city itself. How do you even get there?

Let’s zoom out.

The red circle is the area of the map shown above.

To sail there from the north you had to sail down a very narrow strait called the Bosporus. That strait was very easy to defend both on the land and on the sea.

Moreover, the Bosporus separates Asia from Europe. That means if you wanted to march a land army to Constantinople from Asia…..you couldn’t. You would have to go around the Black Sea, or you would need to at least have ships to transport the army.

That made getting to Constantinople very difficult if you were coming from Persia or Arabia, which was where most of their foes would have been coming from.

What about if you sailed up from the south????

Let’s zoom out again.

Boom. Another extremely narrow strait to the south, the Dardanelles, with its narrowest point being only 1.4km across!!!

This too was heavily controlled by the Byzantines, and it was also how they made a ton of money, controlling trade which went through.

So, you have a peninsula, with the largest and strongest walls in antiquity defending its land border, surrounded by water on three sides, with a massive chain guarding one side, and two incredibly narrow, well-defended straits controlling all naval traffic to the north or south, and the straits also prevent any land incursions from your entire eastern flank.

That is why Constantine picked this place to build his New Rome (Nova Roma). It is one of the most defendable places in the world.

We can zoom one once more.

From an economic standpoint, you can see that Constantinapole is much more centrally located than Rome to the most productive parts of the empire. Closer to Egypt, closer to the Levant, Greece, the Balkans, and the Black Sea.

It is harder to find a better spot to put a city to rule an empire.

Listen to one of my podcast episodes on the Byzantine Empire.

Technically Holy Roman Empire was only self proclaimed as Roman, even as an Empire. For example, Ottomans never used Caesar (Kayser) or Basileus (fasilyus) or Emperor (Imparator) to refer Holy Roman Empire. It was mostly called Kingdom of Germans. Except for the time of Charlemagne, Holy Roman Empire was mostly nothing more than European Union, Emperor did not exactly rule territories of all these small city kingdoms.

In the same vein, Roman Empire (Oriental) saw Kingdom of Germanic tribes claim to Roman legacy as offensive since they considered germanic tribes barbaric. When pope crowned Charlemagne as first Holy Roman Emperor it was because they thought Roman Empire did not have a rule since the ruler was female, Empress Irene. Irene's view was different from traditional Roman view of Germanic-Latin claims to Roman throne, Charlemagne and Irene were to get a royal marriage but Romans looked down on idea of marriage between a Roman and a barbarian who claims to be roman. Marriage never happened; Romans exiled Irene. After that, it was pretty much like this; Oriental Roman Empire did not accept claims of Holy Roman Empire in any ways, neither cultural successor of Oriental Roman Empire aka Ottoman Empire. (I said cultural successor because Ottomans' art, architecture,government type and pretty much everything resembled Oriental Roman Empire. )

In the end, it was never a big deal because two empires did not quite face each other since by that time, Oriental Roman Empire did not extent into Central Europe, and Holy Roman Empire did never expand outside of central europe.

After backstabbing of crusaders aka sack of Constantinople(13th century), Roman Empire had even bigger disdain for Latins and Germanic people of Western Europe. This disdain was to an extent where Roman Empire could accept Turkish muslims to take their legacy rather than self proclaimed Holy Roman Empire. Last Megas Doux of Roman Empire, Loukas Notaras said "I would rather see a Turkish kavuk in the midst of the Constantinople than the Latin mitre." . After conquest of Constantinople, Mehmed II (the Conquerer) was crowned as Caesar(Basileus) of Romans (kayser-i rum in turkish) by patriarchy of Constantinople.

Since Western Europeans turned out to be winners, they wrote history but even term Byzantine was first used by a german historian in 16th century, Byzantine Empire was simply Roman Empire.

Byzantium was the Roman Empire, just the Medieval continuation of it. Why would it need to rebuild itself?

Okay, assuming you’re talking about recovering the West and restoring it to its borders under Theodosius:

Yes, this was 100% possible, given a few crucial details are changed.

1. The plague never strikes. In our timeline, the plague severely diminished the population of the Empire, draining its resources and manpower and basically paralyzing their military-industrial complex. Without this major setback in their conquests, the Romans would be able to replenish their ranks much faster, and get their economy back on track.
2. Justinian brokers a successful peace with the Sassanids. In our timeline, the stick that the Persians kept poking Justinian in the back with was what ultimately caused the reconquest of Italy to take so long. Without this distraction (and maybe the lack of brutal wars that diminished the power of both), Byzantium could conquer the West and probably crush the Arabs’ attacks (or if they had enough resources in this timeline to stay invested in the region, prevent the attacks altogether).
3. Justinian gives Belisarius more men to work with. Manpower shortages were chronic problems for the great general, and he was almost always on the defensive because the Goths had a seemingly endless pool of new recruits, while his army depended on conscripting civilians and receiving small groups of reinforcements on an infrequent basis. Who knows what Belisarius could have done with a Roman army of 50,000 men? Hell, he could have marched from the coast of North Africa to the English Channel to the Rock of Gibraltar and back again.

I must disagree with the general consensus here: that relations between the Franks and Byzantines were bad, and remained bad.

It is true, that the coronation of Charlemagne as Imperator Romanorum was perceived with outrage by the Constantinopolitan court. The Franks had been seen as useful allies - and the Romans had frequently allied with them against the Lombards and Avars, even acknowledging their Romanization.

However, they were viewed by barbarians nonetheless and in the first decade following Charlemagne’s coronation, relations were very strained. This was especially over the fact that Charles was supposed to be the sole Emperor - heir to both Constantinus VI and Romulus Augustulus. Therefore, Irene’s reign as Empress was invalid (since she was a woman), as were the reigns of her successors.

Relations improved later on, however. In 814, both parties agreed to recognize each other as Emperors - just not of the Romans. The Byzantines were willing to acknowledge Charles the Great as Basileus (Emperor) of the Franks, just not Basileus of the Romans. And Charlemagne, in turn, was willing to recognize Nicephorus and his successors as Imperator of the Greeks, but not as Imperator Romanorum.

The reason why the title of ‘Emperor of the Romans’ was so prestigious was the concept of the universal monarchy. As per the concept of ‘One God, One Emperor’ the emperor of the Romans was senior to all other rulers in Christendom - and the Byzantines viewed their state as being the universal monarchy, who held sovereignty over all others.

This warming of relations continued. The Franks and the Byzantines found that they had a lot in common, and formed an alliance to combat their mutual enemies - the Arabs occupying Hispania and Syria, the Norsemen that were raising both territories, the Avars who were hostile to high state, the Bulgars in the Balkans, as well as the pagan Magyars who were invading Central and Eastern Europe. Relations greatly warmed during the reign of Otto I, even as he was crowned Holy Roman Emperor in 962. This was cemented with a marriage between Otto’s son, the future Otto II, and Princess Theophanu, the niece of Emperor John I.

Moreover, during the 10th and 11th centuries both forces had a distrust of the Papacy and their Norman allies, who had inflicted a humiliating defeat upon Alexios I Komnenos in 1081. The Outremer became a point of contention between the HRE and the Byzantines, as Emperors John II and Manuel I sought to impose their suzerainty over the Crusader states. Frederick Barbarossa became an enemy of Manuel I Komnenos over the latter’s alliance with the anti-Frankish Lombard League, and threatened to assault Constantinople during the Third Crusade.

Relations warmed during the reign of Barbarossa’s son, Henry VI, however. Henry married his brother Philip to Irene Angelina, daughter of Isaac II Angelos. The Holy Roman Empire was particularly upset with the ‘Latin Empire’ that was formed after the Fourth Crusade and their refusal to submit to the Holy Roman Emperor. To this end, Frederick II married his daughter to the Nicaean Basileus John III Doukas Vatatzes in order to form an anti-Papal alliance. However, by the end of the 13th century the Byzantines were once again in decline and were reduced to a regional Balkan power before their eventual demise in 1453 which made relations minimal. During his travels in Europe, however, Manuel II Palaiologos was welcomed at the courts at multiple European monarchs- among them the future Holy Roman Emperor Sigismund of Luxembourg.

“Byzantine” is completely a fabricated word. It became popularized during the mid-17th century by scholars such as Montesquieu. Following a western European tradition that extended back to the earyl middle ages, Montesquieu regarded the empire at Constantinople as “cor-rupt and deca-dent.”

The English scholar Gibbon treated the empire after the 6th century as an “epic of unrelieved de-gradation and cor-ruption.” ( Decline and Fall of the Roman Empire )

It is also not possible to find the word “Byzantine” in any terminology such as, “Byzantine empire, emperor, throne, army, territory” etc. There was only the “Eastern Roman Empire, or Romania”. The fundamentalist Anglo-Saxons and Judeans simply fabricated the word due to political and religious reasons.

During the enlightenment era, Catholic church did not have a positive view on the Orthodoxy. Especially pro-enlightenment despots were si-ck of the idea of a religious “Byzantine spirit”.

According to them, “Byzantine” history was a collection of worth-less de-clamation, miracles, con-vulsion, rebellion and dis-honor ( Voltaire / Montesquieu ). In other words, it was nothing but a sad ending of the glorious Roman history.

When Charlemagne was crowned as the Roman emperor, he officially rejected the east as “true Romans”. The fabrication of the word “Byzantine” was necessary for the Anglo-Saxon/Protestant Christianity as a solution, or justification for the interests of Catholic western Europe against its enemy (Orthodox east), secterian war and the struggle against Islam.

That is why, after capturing Constantinople, Venetians and other Catholic crusaders pillaged the city for three days. They looted monuments and buildings. The scale of plunder, massacre and ra-pe committed by the Latin soldiers was at such an unimaginable level.

The French, Flemish and Germans destroyed everything without any segregation, ra-ped the nuns and killed the priests and monks. They also expressed their hate and dis-gust for Orthodox Romans by tarnishing the holiness of Hagia Sophia. They considered all of this as an act of revenge for the seperation of Orthodoxy from Catholic church and did not feel any regret or remorse.

Empire Strikes Back! This is one of my favourite pet peeves.

The answer is basically Yes, with three provisos:

1. The Justinianic Plague never strikes. The Plague of Justinian (541–542) was a pandemic that afflicted the Eastern Roman (Byzantine) Empire, especially its capital Constantinople, the Sassanian Empire, and port cities around the entire Mediterranean Sea. One of the deadliest plagues in history, this devastating pandemic resulted in the deaths of an estimated 25 million (at the time of the initial outbreak that was at least 13% of the world's population) to 50 million people in two centuries of recurrence. In 2013 researchers found that the cause of the pandemic was Yersinia pestis, the bacterium responsible for bubonic plague and the Black Death 800 years later.
   
   The plague's social and cultural impact during the period of Justinianus has been compared to that of the similar Black Death that devastated Europe 600 years after the last outbreak of Justinian plague. It led in the final loss of Britannia to Barbarians.
2. Belisarius and Narses are given free hands. The two greatest generals of the era fell victims of palace intrigues and plotting. Had they been given more resources and free hands, they most likely would have conquered the rest of the lost lands. Had they been given more men and money, it is likely they would have reconquered Gallia from Merovingian Franks. The Early Byzantine armies were cavalry based armies optimized on fighting Barbarians.
3. Islam never rises. From its very beginning, Islam was the greatest menace of the Empire, and from 633 on, the Byzantine wars concentrate mainly on defensive fight against Islamic armies - first Arabs, Berbers, Saljuqs, Turcomans, Mamluks and finally Ottoman Turks. This defensive fight basically drained the Empire. Without Islam, and peace secured with Sassanid Persians, the Empire could have concentrated and projected its efforts on reconquering and reconsolidating the lands of West.

—-

Then the big question: Okay, so the plague never strikes, the victorious generals lead the cataphracts and kavallarioi from victory to victory and Islam never rises. What will the rejuvenated Roman Empire do? Will the extant territories suffice - or will it attempt to expand its sphere North, towards German, Bohemian, Moravian, Pannonian and Sarmatian lands?

What would the new, unified Europe look like? Would Greek have superseded Latin eventually also in Western Europe, and would we all be Orthodox Christians today? Will Constantinople send missionaries to the Sarmatian and Alan lands and to Scandinavia?

What we know today is that Finland is the northernmost outpost of the Byzantine cultural sphere: while majority of Finns are Lutherans, Orthodoxism is the other national church and the traditional religion of Karelians. The Orthodox influence has been deep, and extended to Tavastian lands (Finnish Häme, Russian Yemi): there is an ancient fortified hill named Kapatuosia near Lahti, deep in central Finland. The etymology is Cappadocia - the heavily fortified heartland of the Empire in the 11th and 12th century. It was an Orthodox bulwark in Finland against Pagan Tavastians and Catholic Western Finns. Many of the place names near Lahti are clearly Karelian and Orthodox. So the Imperial influence was strong even more than 3000 km off the Imperial heartlands!

In the nineteenth century, a racist German historian made hell of a mess and confusion by pulling out the term <<Byzantine>> out of his sleeve. Between the Fourth Century A.D., when Constantine founded Constantinople on the site of the ancient Greek city of Byzantium, and the eighteenth century, NO ONE ever used of heard of the “Byzantines” of the “Byzantine Empire.” For the people living in that part of the world corresponding to the Eastern part of the Ancient Roman Empire, they simply continued being the Roman Empire, and its citizens, Romans. A legal proof of the legality of the Roman Empire was the fact that the crowning of Charlemagne as Emperor of the Holy Roman Empire by the pope of the Church in Rome was denounced as illegal by all the jurists at the time. According to the Roman law, only the emperor in Constantinople had the power to crown a co-emperor. After a couple of decades, the title of Charlemagne was re-negotiated and he became “sibling-emperor.”

During the Middle Ages, the Roman Empire (not Byzantine) was the envy of Europe. Many Europeans who had visited Constantinople and became jealous of its splendor started calling the empire the “Empire of the Greeks.” since Greek was the language spoken colloquially across the empire. Out of jealousy, they called “Greeks” the inhabitants of the empire. The growing ascendancy of the Northern European nations at the end of the Middle Ages led to an arbitrary reinterpretation, in which the Greeks were not worthy of the Roman heritage and their actual and continuous connection with the Roman Empire was arbiratrily severed, and made it seem like the glorious Roman Empire had fallen only to have its place opportunistically taken over by these Byzantines coming out of nowhere.

As of your question, the Roman Empire would definitely fall in 1453. However, for about a century after the fall of the Western part of the empire, the Roman emperors unsuccessfully attempted to recover the lost territories. Unlike the Germanic tribes that the Republic and early imperial legions had defeated, the Germanic tribes ion the fifth century were completely familiar with the Western and Eastern Roman warfare, and they had learned how to defeat them even in open battlefields. Actually, many Germanic warriors had served in either the Western or Eastern Roman legions and shared their knowldge with their fellow warriors. In conclusion, the Eastern Roman Empire had no realistic chances of recovering the lost lands of the Western Empire because of the logistic difficulties of maintaining a huge army on the field, because the people in the former Western provinces had been mistreated by the Eastern Roman legionaires, so they switched allegiances with the Germanic warriors, and because the Germanic warriors made every victory costly in men and resources.

It was both, and, more pertinently given the premise of your question, the latter. Roman emperors had stopped using Rome as a capital due to pressing concerns elsewhere, near exposed frontiers. For example, during the four-member college of emperors known as the Tetrarchy (293–311 or so), there were four more or less permanent imperial residences (Nicomedia, Mediolanum, Thessalonica, and Augusta Treverorum), none of them Rome. This preceded the refounding of the ancient Greek city of Byzantion as New Rome (soon known as Constantinople, after the emperor responsible) in 324 (official dedication in 330). Constantinople had greater permanence and longevity as an imperial residence and imperial capital, but at first it was not the only one: there were still usually two or more emperors, and those in the west tended to rule from Mediolanum (Milan) and Ravenna more often than Rome (although, contrary to popular belief, Rome was not completely abandoned by the emperors); an indication of the growing importance of Constantinople is that it, like Rome, acquired an imperial senate: now there were two.

While two senates and two imperial courts suggest two Roman Empires and they are often referred to as such, technically the Roman Empire remained one, under dual administration in its respective eastern and western parts. If there was a vacancy on the throne of either, it was automatically filled by the incumbent in the other. “Western Roman Empire” and “Eastern Roman Empire” (worse, the more modern “Byzantine Empire” or “Byzantium”) are primarily retrospective terms, although something like that had been employed unofficially and descriptively whenever a differentiation had been necessary. After 480 there were no more Roman emperors based in the west, but for almost another millennium there was a Roman emperor (or more than one) based in the east, usually at Constantinople. It was the same institution, state, name, title, body of citizens, continuing on in the surviving parts of the empire — whose territories expanded and contracted over time (at one time recovering much of the Roman western Mediterranean).

So, legally and legalistically but also factually in every conceivable way, the (Eastern) Roman Empire (“Byzantium”) was just the Roman Empire surviving in the East. As Roman culture had adapted before (most notably with the triumph of Christianity), it continued to do so now: the Greek culture that had always been dominant in the Roman East was eventually reflected (after a drawn out gradual process in different spheres) even in the most formal and conservative institutions and settings (laws, army, coinage, etc). In 800 the Roman pope created (without legal precedent) a new Roman emperor in the West in the person of his protector, the king of the Franks and Lombards, laying the foundation for what will later be called the Holy Roman Empire — which claimed to be in a sense the (Western) Roman Empire restored. Papal and Frankish (and post-Frankish) propaganda now tended to depict, due to both cultural and political factors, the (Eastern) Roman Empire as Greek (which it never considered or called itself, for all that it reveled in most aspects of Greek culture). But that external, biased or uninformed treatment is irrelevant. In 1204, the Fourth Crusade was diverted to Constantinople in part because of conflict over the (Eastern) Roman throne. The result was Crusader occupation of the (Eastern) Roman capital for 57 years (1204–1261, the so-called “Latin Empire”) and the splintering of the (Eastern) Roman state into several fragments (centered on Nicaea, Trebizond, and in Epirus). All three claimed the Roman imperial legacy (and had excellent institutional and dynastic grounds to do so, unlike the “Latin Empire”), but Nicaea recovered Constantinople in 1261. The Constantinople-based (Eastern) Roman Empire was eliminated by the Ottoman conquest in 1453. The Empire of Trebizond survived longer, until eliminated also by the Ottomans in 1461. Those dates mark the end of the original uninterrupted (even if re-focused and at times displaced) existence of the Roman state.

The “Holy Roman Empire” in the west survived until 1806, but it was not really part of the same uninterrupted tradition, even though it made a claim of institutional continuity. More flimsily, some modern revisionists have suggested that Ottoman Turkey was also a continuation of the Roman Empire. It was not, and the occasional and secondary use by the Ottoman sultan of the title of Roman emperor was an assertion of rule over the former Roman Empire and of prestige. This does not change the fact that the Ottoman Empire is a completely different state formation of differing character and religious and cultural foundation, which conquered the (Eastern) Roman Empire’s remnants and did not maintain (but actually terminated) the last surviving Roman political institutions — like the senate of Constantinople.

You can find more details in the related answers below:

The so-called “Byzantine Empire” is also known (more accurately) as the Eastern Roman Empire. It called itself the Roman Empire and was indeed simply the final stage of the development and existence of the Roman Empire. It is usually said to have lasted from AD 330 (when the emperor Constantine I officially dedicated the city of New Rome/Constantinople as an imperial residence) to 1453 (when the emperor Constantine XI was killed and the city was captured by the Ottoman Turks). However, institutionally the Eastern Roman Empire was just a continuation of the Roman imperial tradition going back to the first emperor, Augustus (r. 30 BC—AD 14).

The twin formation of the Western Roman Empire ended with the deposition of the emperor Romulus in 476 and the death of the emperor Nepos in 480. In case you are wondering when the Eastern and Western Roman Empires split, there is no clear answer. It was not 330, because Constantine I ruled the entire Empire from 324 to 337. Nor was it 337, when the Empire was divided among Constantine’s three sons, because it was reunited again after this (and it had been divided before). It is usually said that the division took place on the death of the emperor Theodosius I in 395, who was succeeded by one son (Arcadius) in the East and another son (Honorius) in the West. However, technically it was one Roman Empire all along, under the administration of different (usually two) emperors in different (usually two) parts — when the throne became vacant in one half, technically the surviving emperor in the other became sole ruler of the Empire. This happened several more times in the 5th century (most notably with Theodosius II in 425, Marcian in 456–457, and Leo I in 457, 465–467, and 472–473) — and if one considers these reunifications too fleeting to be important, one should remember Theodosius I had only ruled the entire Roman Empire for a few months before his death, in 394–395.

For most of its existence, the Eastern Roman Empire did not control Rome, except for a period from 536 to 754/772/776/781 (depending on how you count). The vast majority of its population was Greek speaking (as it had been throughout the Roman period), and Greek supplanted Latin in the laws in the 6th century and in imperial decrees in the early 7th century. The Roman identity of the population as a whole (and this is true throughout the Roman Empire, not just its eastern half) goes back at least to the grant of Roman citizenship to all free inhabitants of the Roman Empire in 212. The capital remained at Constantinople throughout the existence of the Eastern Roman Empire, except for the period 1204–1261, when it was occupied by the so-called “Latin Empire,” established by the Fourth Crusade (this political formation called itself Empire of Constantinople or Romania, from the Greek term for “Land of the Romans”). In 1204–1261, the Eastern Roman imperial tradition was maintained by a successor state centered on Nicaea (Nikaia) in Asia Minor, which recovered Constantinople in 1261. Rival successor states were established at Trebizond in Asia Minor (1204–1461) and in Epirus in northwestern Greece (1205–1449, although this last only aspired to Roman emperorship in 1224–1230/1242). Some claim to the Roman imperial legacy was made by the emperors of Bulgaria (from 913) and of Serbia (1345–1371/1373).

The “Holy Roman Empire” claimed the legacy of the Roman (or Western Roman) Empire, but after a significant hiatus (480–800) and in changed circumstances. It was not originally referred to by this name, and it is also sometimes called the “Frankish Empire” and after that the “German Empire” (but these were never its formal names, and it is a different state formation than the modern German Empire of 1870–1918). Long dependent on the support of the Frankish kings of the Carolingian Dynasty, the pope crowned the Frankish king Charlemagne emperor (implicitly or explicitly of the Romans) on Christmas Day, 800. Part of the rationale was that at this moment the throne of Constantinople was occupied by an empress, for which there was no Roman legal precedent, so it could be said to be vacant; there was no precedent for a pope creating an emperor. Charlemagne and his heirs were now in effect emperors of a renewed (Western) Roman Empire, and despite the occasional diplomatic scuffle, did not reject or deny the Eastern Roman Empire. Hard pressed by other enemies, the Eastern Roman emperor conceded the imperial dignity to Charlemagne, but only as emperor of the Franks. Charlemagne was big enough to turn a blind eye to this, but others (most notably his great-grandson Louis II) did not, and friction and recrimination ensued, with the Eastern Romans refusing to recognize the Frankish emperors as Roman or even emperors, and the Frankish emperors suggesting the Eastern Roman emperors were Greek kings.

Charlemagne had crowned his son and heir Louis the Pious emperor in 813, but after Charlemagne’s death in 814, Louis insisted on getting crowned anew by the pope, creating a dangerous precedent, with coronation by the pope becoming a prerequisite for the (Western) emperor’s standing as such. Delayed coronations and the increasingly chaotic politics of the Carolingian dynasty meant vacancies in the imperial succession in 877–881, 887–891, 899–901, 905–915, and 924–962. In 962 the East Frankish (German) king Otto I got himself crowned emperor by the pope, continuing the imperial tradition established by Charlemagne, and making the imperial dignity inextricably attached to the East Frankish/German kingship. The German king was also king of Italy (from 963) and of Burgundy (from 1032). The personal union between these three kingdoms therefore constituted the new iteration of the Roman Empire in the West. Otto’s imperial coronation in 962 is often cited as the beginning of the Holy Roman Empire, although it was not yet called this, and it explicitly continued the imperial tradition established by Charlemagne in 800. Imperial status still depended on coronation by the pope, something becoming problematic after emperors and popes began to clash, starting with the Investiture Controversy in the second half of the 11th century. The Empire was always implicitly Roman, but that was not always explicitly stated in its name (in fact, it is unclear if it had a formal name, besides “Empire.” By 1157 it was referred to as the “Holy Empire” (Sacrum Imperium), by 1254 as the “Holy Roman Empire” (Sacrum Romanum Imperium), and by 1450 as the “Holy Roman Empire of the German Nation” (Sacrum Imperium Romanum Nationis Germanicae). The Holy Roman Empire (and likewise its three constituent kingdoms) had no true capital, and imperial residence at Rome was rare, usually associated with a brief stay for the imperial coronation. Rome itself was actually under papal control, ever after the creation of the Papal States by the Donation(s) of Charlemagne’s father Pepin in 754/756. The Papal States became effectively independent from the Empire in 1177; they were largely eliminated during the unification of Italy in 1860–1870, except for Vatican City.

Recurrent conflicts with the papacy undermined the power and de facto hereditary succession of the monarchs, and there followed a long period during which elections brought different noble houses to the throne on different occasions (most notably the Habsburgs, Luxemburgs, and Wittelsbachs); in 1328 it was decreed that the elected king of Germany was entitled to the title of emperor even without being crowned by the pope, a practice formally asserted in 1508. The last emperor crowned by the pope at Rome was Friedrich III (Frederick III), in 1452, and the last emperor crowned by the pope (at Bologna) was Karl V (Charles V), in 1530 (unless one counts Napoleon I Bonaparte in 1804, but that was as emperor of the French). Karl V was also the last Holy Roman emperor to actually control Rome, having conquered it from the pope in 1527. The religious divisions and political conflicts caused by the Protestant Reformation in the 16th century and the Catholic Counter-Reformation in the 17th century led to territorial losses (Switzerland, the Netherlands) and the increasing autonomy of the various components of the Empire, transforming it into a rather loose confederacy.

After 1438 the throne (even if still elective) was monopolized by the Habsburg family, based primarily in Austria, until it became extinct in the male line in 1740. Subsequently, two sons-in-law of the last two Habsburg emperors, the duke/elector of Bavaria and the former duke of Lorraine were elected in quick succession, the latter establishing the House of Habsburg-Lorraine, which monopolized the throne from 1745 to 1806. In the context of the French Revolutionary Wars, the Holy Roman Empire lost its few remaining Burgundian and Italian possessions, as well as the lands west of the Rhine, and Napoleon’s France proceeded to interfere in its affairs. Having already declared himself emperor of Austria in 1804, the last Holy Roman emperor formally declared the Holy Roman Empire dissolved in 1806. The Habsburgs continued to rule the Austrian Empire until 1918 (they were also kings of Bohemia, of Galicia-Lodomeria, of Hungary-Croatia, and until 1866 of Lombardy-Venetia). In 1815–1866 they also presided over the German Confederation, until this was dissolved and eventually replaced by the new German Empire under the leadership of Prussia.

While both Empires ultimately hearkened back to the ancient Roman legacy, they were quite different in many ways, as should be apparent from the above.

The debate over whether the Byzantine Empire was a continuation of the Roman Empire or a new entity altogether has persisted for centuries. The Byzantine Empire, also known as the Eastern Roman Empire, thrived for over a millennium after the fall of the Western Roman Empire in AD 476. To understand the connection between the two, one must consider various facets of their existence.

Historical Continuity

The most evident argument for the Byzantine Empire being a continuation of the Roman Empire is its historical lineage. The Roman Empire had, for administrative purposes, been divided into Eastern and Western halves by Emperor Diocletian in the late 3rd century AD. While the Western half fell in 476, the Eastern half continued uninterrupted. The citizens of this empire, based in its capital Constantinople (modern-day Istanbul), referred to themselves as "Romans" and their land as the "Roman Empire" even until its fall in 1453.

Cultural and Administrative Legacy

Many aspects of Roman governance, law, and bureaucracy persisted in the Byzantine Empire. The Byzantines inherited the Roman system of provincial administration, and the Justinian Code (Codex Justinianus) of the 6th century was a compilation of Roman legal traditions. Moreover, Latin remained the official language of the Byzantine state until the 7th century.

Religious Evolution

Christianity, which had become the state religion under the late Roman Empire, was central to Byzantine identity. However, there were significant theological shifts, with the East and West frequently at odds, culminating in the Great Schism of 1054, which divided Eastern Orthodoxy and Roman Catholicism.

Cultural and Linguistic Shifts

Over time, the Byzantine Empire began to exhibit distinct characteristics. The Greek language took precedence over Latin, especially after the 7th century. Additionally, Byzantine art and architecture, while rooted in Roman antecedents, evolved unique features, such as the iconic domed basilicas.

Byzantium (actually Βυζάντιον, Byzántion in Greek) is the city. The empire was never officially known as “Byzantine,” — it was, in the eyes of its emperors and people, simply the Roman empire. The city was renamed Constantinopolis when Constantine made it the seat of his government in the year 330, though most Greek speakers knew about it’s old name… just as plenty of New Yorkers know that “old New York was once New Amsterdam”.

The name “Byzantine empire” was a term coined first by German historians in the sixteenth century, well after Constantinople had fallen to the Turks. It was popularized by European scholars who were ideologically or aesthetically attracted to the Rome of Caesar and Cicero but not the New Rome of the Greek-speaking, orthodox, and “byzantine” East Roman Empire. See also Why is the Eastern Roman empire called Byzantine empire?

The transformation of Rome into Byzantium was a much needed Roman strategic regroup from the West to the East in the 4th century. The principal reasons underlying this strategic shift arose under the pressure of several developments in the East that would eventually place greater importance on the Eastern portion of the Roman Empire.

In Late Antiquity, extensive swathes of the Western Roman Empire became all the more difficult to keep due to pressure from barbarian invasions and migration. On the other hand the Pars Orientis, the Eastern part of the Roman Empire was much richer and offered a more strategic position with the city of Byzantium located in its centre. The original city known by the name of “Byzantion” had been a Greek colony for many centuries. It was later renamed to Nova Roma when Emperor Constantine the Great made it his new capital in 330 C.E.

The city had its bonuses as it was surrounded by sea and it could easily be defended by its strong land walls and a competent navy. Barbarian invasions mostly had their origin in the East, hence the selection of Byzantium conferred the Eastern Roman Empire more stopping power against successive waves of invaders.

Byzantium was at the centre of the Eastern Greek-speaking world, rich in Christian tradition and history. Emperor Constantine strategically set his crosshairs on Byzantium because his Christian subjects were starting to play an ever-increasing role in the empire's pressing matters now that Christianity became the official Roman religion. Constantine had also wanted to utilise Christian zeal against the Persian superpower of the Sassanids which was equally competing as Rome for world domination or “dominium mundi”.

The new capital also rested on the crossroads of two continents and it was a busy tradehub with vital commerce routes reaching from the Black Sea, the Middle East and Asia.

Yes, the Byzantine Empire was the continuation of the Roman Empire.

Because it survived the fall of the Western Roman Empire it could exist until the fall of Constantinople to the Ottoman Empire in 1453.

It basically was the Roman Empire because it saw itself as the Roman Empire and its citizens continued to speak Greek and use Roman law and administration.

But of course, this remains speculation among historians.

The term “Byzantium” is often considered an incorrect name for the Eastern Roman Empire, and this viewpoint is supported by renowned historian D.J. Georgacas in his book “Names.” Let’s delve into why this is the case and explore the fascinating reasons behind it.

Firstly, it’s essential to understand the historical context. The Eastern Roman Empire, commonly referred to as Byzantium, was the continuation of the Roman Empire in its eastern territories after the fall of the Western Roman Empire in 476 CE. However, the empire itself never referred to itself as Byzantium. Instead, its inhabitants identified themselves as Romans or simply as the Roman Empire.

So why did the name “Byzantium” come into existence? The term can be traced back to the ancient Greek city of Byzantium, which stood on the site of the modern-day city of Istanbul. In 330 CE, Emperor Constantine I chose Byzantium as the new capital of the Roman Empire, renaming it Constantinople in his honor. This decision marked a significant shift in power from Rome to the east.

Over time, as the Western Roman Empire faded into history, the Eastern Roman Empire became known as the Byzantine Empire, primarily due to the influence of early medieval historians and scholars. These individuals sought to differentiate between the two periods of Roman rule and used the term “Byzantine” to describe the empire’s later phase.

However, this classification has faced criticism for several reasons. Firstly, it creates an artificial divide between the Roman Empire and its later incarnation, implying that the Byzantine Empire was a separate entity altogether. This perception undermines the continuous nature of Roman civilization, which endured for over a millennium.

Furthermore, using the term “Byzantium” can overshadow the significant contributions and achievements of the Eastern Roman Empire. This empire maintained Roman traditions, institutions, and culture while also developing its own distinct character. It witnessed remarkable advances in art, architecture, law, and governance. By referring to it as Byzantium, we risk neglecting these achievements and reducing its historical significance.

In recent years, there has been a growing movement among historians and scholars to rectify this misnomer and return to using the term “Eastern Roman Empire.” This shift aims to reestablish the empire’s rightful place in history and acknowledge its integral role in shaping the medieval world.

Constantine’s (r. 324–337) decision to found a new imperial center in the pars orientalis of the Roman Empire was neither arbitrary nor a major breakthrough. In this as in other issues, Constantine followed the footsteps of Diocletian (r. 284–305), the reformist emperor who put an end to the so-called 3rd century crisis. When developing the tetrarchy, Diocletian kept for himself the eastern part of the empire and made the city of Nicomedia in Bithynia his seat. This means Rome had ceased to be an/the emperor’s seat for some time.

As a whole, the pars orientalis was more densely populated and had bigger, wealthier, and more ancient cities (Ephesus, Smyrna, Nicaea, Alexandria, Antioch, Caesarea). In this sense, politics merely followed and reflected the existing demographic and economical situation, not the other way around. Secondly, the empire faced increasingly severe military issues in the east that required the emperor’s presence nearby. The major threat was the newly formed Sassanian dynasty, which was more aggressive than the Parthians. The Danube frontier was also under pressure from barbarian tribes.

As far as Constantine is concerned, the eastern part of the empire was also more Christianized and alien to the stiff, conservative Roman senate. The first Christian emperor could count on easterners more.

It’s said that Constantine pondered the exact location of his new seat for some time. Troy and perhaps Chrysopolis appear in the primary sources as options. Byzantium prevailed, though, because it combined a series of advantages:

• Geographically, the city was situated at the crossroads of two continents—Europe and Asia—and two seas—the Black Sea and the Mediterranean Sea. Thus, he who held it could control communications, trade, and transportation. The ports and customs of Abydos and Hieron, south and north of Constantinople respectively, were the gates of regional—one could even say global—trade.
• The city could only be accessed by land from its western side, which was soon fortified. On all other sides it was surrounded by sea. Thus, a full blockade, which was necessary for any siege, was very difficult to maintain. Most of the times Constantinople found itself besieged either by foreigners (Bulgarians, Arabs) or by usurpers (e.g. Thomas the Slav), it could be resupplied by sea and thus avoid starvation and diseases.

Byzantium was an ancient Greek city that was founded by colonists from Megara around 657 BC. It was located on the European side of the Bosporus, the strait that connects the Black Sea and the Mediterranean Sea. It was a strategic location for trade and commerce between Europe and Asia.

The Roman Empire conquered Byzantium in 196 BC and renamed it Byzantion. Later, in AD 330, the Roman emperor Constantine I made Byzantion his new capital and renamed it Constantinople, meaning "the city of Constantine". He also made Christianity the official religion of the empire.

Constantinople became the center of the Eastern Roman Empire, also known as the Byzantine Empire, after the fall of the Western Roman Empire in the 5th century AD. The Byzantine Empire preserved and developed the culture, law, art, and literature of ancient Rome and Greece. It also spread Orthodox Christianity to Eastern Europe and Asia Minor.

The Byzantine Empire was often at war with its neighbors, such as the Persians, Arabs, Turks, Bulgars, Slavs, Crusaders, Mongols, and Ottomans. It also faced internal challenges, such as religious schisms, political factions, civil wars, and economic decline. The empire reached its peak of power and prosperity under Emperor Justinian I in the 6th century AD and under Emperor Basil II in the 10th century AD.

The Byzantine Empire finally collapsed in 1453, when the Ottoman Turks captured Constantinople after a long siege. The Ottomans renamed the city Istanbul and made it their capital. The legacy of Byzantium lives on in the modern nations of Greece, Turkey, Bulgaria, Serbia, Romania, Russia, and others that were influenced by its culture and religion.

So Byzantium was both a successor and a predecessor of the Roman Empire. It was also a part of the Roman Empire until it split into two halves. It was related to Greece by its origin, language, and heritage. And it was not simply anything. It was a complex and fascinating civilization that lasted for over a thousand years.

What’s a “blood empire”?

I’m guessing you mean that somehow the Roman Empire was held together by some kind of kinship ties. The entire point of an empire is that it’s not about a single nation. That’s what distinguishes an empire from a kingdom. An empire is trans-national. A “blood empire” would be an oxymoron.

Rome had already changed its religion. The Roman Empire was founded on the syncretic, polytheist Roman religion, incorporating all local deities into a pantheon. As long as the locals paid at least some kind of lip service to Jupiter, they got to keep doing what they were doing. But the later Roman empire, both West and East, was Christian. The two parts were more religiously unified than they had been under Augustus.

Culturally Constantinople was distinct from Rome (or the other Roman capitals that came later), but remember that the name was Constantinople. It was founded by a Roman emperor. It was a Roman city. It happened to speak a different language, but the Roman empire incorporated many languages: Egyptian, Hebrew, Greek, and many others. Constantine named it after himself using Greek, because Greek was a prestige language in Rome.

The Roman empire was proud of its cultural diversity. It ruled Africans, Mesopotamians, Europeans, on up towards the Baltics. All of these cultures changed over the centuries of empire. It would be weird if they didn’t. Their distinctiveness wasn’t un-Roman; it was deeply Roman.

Around the turn of the 4th century AD, the emperor Diocletian created an administrative division in the Roman empire. He split it in half and created parallel administrations, with a senior emperor and a junior emperor for each half. The emperors were to be co-rulers of a single empire and act in concert as necessary but independently administer the parallel bureaucracies in their own divisions. The scheme wasn’t particularly effective (sometimes one of the emperors effectively ran the whole show, sometimes the eastern and western emperors acted entirely independently), but this was the beginning of not separate empires, but rather two divisions of a single empire. Nevertheless, it’s convenient to call them the eastern and western empires.

In 476 AD, the line of emperors in the west went extinct and the empire in the west effectively ended. Indeed, the authority of the western emperor was pretty much limited to portions of Italy anyway. The eastern empire survived, however. There was a clear legal and administrative continuity with the old, united empire, but was already somewhat culturally distinct and continued to change in various ways. Again, for the convenience of historians, the eastern empire is usually called the Byzantine empire, after one of the names of its capital (though, ironically, the city of Byzantium was renamed Constantinople when it became the eastern capital). “Byzantine” was never used by anyone at the time as the name of the empire. Rather, that name was coined by historians after the empire had fallen.

The Holy Roman empire was essentially an attempt to claim the legal legitimacy of the Roman empire in the west. The imperial seat had fallen vacant in the fifth century, but the Frankish king Charles (or, as everybody calls him now, Charlemagne) prevailed on the pope, based on various legal pretexts, to grant him the title of emperor. This worked out well for both parties. Charlemagne got a legal pretext to enlarge his kingdom as much as possible and put himself on an equal diplomatic footing with the emperors in the east (or, at the time, Christmas Day 800 AD, the empress), while the pope was able to assert the authority to determine who got to be emperor. The title of emperor passed through various rulers, mostly governing Germany and eastern France, until the early 19th century.

To quote the famous line, “The Holy Roman Empire was neither Holy, nor Roman, nor an Empire” - Voltaire

The Roman Empire was centered on Rome, Italy, and is considered to have lasted from 27BCE/BC until 476CE/AD. It was formed from the Roman Republic before it, with roots stretching back from the 8th century BC. The Eastern Portion of the Roman Empire, also known as the Byzantine Empire, survived the fall of the Western Empire until 1453CE/AD.

Roman People:

The Roman Empire in 117CE/AD:

The division of the Empire:

The Holy Roman Empire had its roots in the Roman Empire, as the Franks, a Germanic People who would eventually lend their name to France, were brought into the Northern edges of the Roman Empire as mercenaries and vassals to defend the borders from more destructive Germanic peoples further North. After the fall of the Western Roman Empire in 476, Europe descended into the so-called Dark Ages, in which literacy, communication, trade, and many forms of knowledge declined. In this period, also known as the Early Middle Ages, the kings of the Franks conquered territory roughly corresponding to France, Belgium, and Western Germany. Eventually, the famous king Charlemagne rose to the throne, and on December 25th, 800CE/AD, the pope crowned Charlemagne as the King of the Franks,

attempting to give the impression that the ancient Roman Empire had risen again and the union of the Church and the Empire would reclaim the previous empire.

Charlemagne’s Empire in 800 (in orange):

After the death of Charlemagne’s son, though, the Frankish Empire split into three. The western part became France, the Central part, called Lotharingia, would become a few kingdoms like Alsace, Lorraine, and Burgundy. Only the eastern part, corresponding mostly to modern Germany, would come to be called the Holy Roman Empire (though it wouldn’t be called that for centuries yet). In the following centuries, it lost lots of power to feuding princes, bishops, and pillaging viking raiders, eventually becoming confined to the area roughly of modern Germany and being a weak, decentralized, ineffective government until its conquest and dissolution by Napoleon in the early 1800s.

The Empire in 1789:

Byzantium was the Roman Empire during the Middle Ages. After the west fell the eastern empire survived until 1453. The Eastern Roman Empire did succeed in reconquering lost western territories of Italy, North Africa, and part of Spain.

The problem came when the Eastern Romans had to deal with invasion from multiple enemies. The Eastern Romans lost huge chunks of territories in North Africa and the Levant to the Arabs during the Early Muslim Conquests. The Lombards took many Eastern Roman territories in Italy and their last outpost in Italy, Bari was lost in 1071 to the Normans.

That would depend on your point of view. The Eastern Roman Empire didn't want to restore the Western Roman Empire when Belisarius reconquered Rome, Perugia and Ravenna from the Ostrogoths in 535 AD. That would be a dumb move from their perspective. So they simply reorganized it as the Exarchate of Ravenna. For all intents and purposes, the “Byzantines” were the Roman Empire.

Then in 568, the Lombards invaded Italy. The exarch or governor allowed them safe passage through the exarchate to conquer what they later called the duchies of Benevento and Spoleto. However the Greek speaking cities of southern Italy and Sicily were still controlled by the empire.

Every now and then the Lombards would act up and the Papacy and Exarchate would give them a few thousand gold solidi. And they'd go away. However in 754 AD, the Lombards killed the last exarch. They surrounded Rome and demanded a tribute of one gold solidus coin per Roman.

The pope called for help however Constantinople was too far away. Then one man answered the call, Pepin the Short king of the Franks. He came down from across the Alps and brought the Lombards to heel. He converted them all to Nicene-Chalcedonian Christianity.

Then in 800 AD, Pepin's son Charlemagne was crowned Emperor of the Romans by the Pope. All that Empress Irene could do was send a strongly worded letter to the pope and Charlemagne.

The country of Byzantium, also known as the Byzantine Empire, was actually a continuation of the Eastern Roman Empire rather than a separate entity. After the fall of the Western Roman Empire in 476 AD, the Eastern Roman Empire, with its capital in Constantinople, continued to thrive for nearly another thousand years.

The Byzantine Empire reached its peak under the rule of Emperor Justinian I in the 6th century. During his reign, Justinian sought to restore the glory of the Roman Empire by reconquering lost territories in the West and codifying Roman laws into the Corpus Juris Civilis, also known as the Justinian Code.

However, the Byzantine Empire faced numerous challenges throughout its existence, including invasions by various barbarian tribes, religious schisms such as the Great Schism between the Eastern Orthodox Church and the Roman Catholic Church, and conflicts with neighboring powers like the Arab Caliphates and the Ottoman Turks.

In 1453, the Byzantine Empire finally came to an end when Constantinople fell to the Ottoman Turks led by Mehmed II. The city’s defenses were breached after a lengthy siege, marking the final demise of the once-mighty empire. The fall of Constantinople not only ended the Byzantine Empire but also marked the end of the Middle Ages and the beginning of the Renaissance.

After the fall of Constantinople, some Byzantine scholars and artists fled to Italy, bringing with them valuable knowledge and manuscripts that would later contribute to the intellectual and cultural flourishing of the Italian Renaissance. The fall of Constantinople also had significant geopolitical implications, as it allowed the Ottoman Empire to expand further into Europe.

All in all, the Byzantine Empire was not absorbed into the Roman Empire but rather represented the continuation of the Eastern Roman Empire that endured for centuries after the fall of the Western Roman Empire. Its legacy lives on in the form of its art, architecture, literature, and legal traditions, which have had a lasting influence on Western civilization.

Part of speech.

Byzantine is an adjective. Byzantium is a noun. Byzantine means related to or pertaining to Byzantium. Byzantium is the name of a place, an ancient Greek colony which was later heavily rebuilt and renamed Constantinople, though the old name was occasionally used as an archaic nickname for the place.

Now, both of those words carry far more complicated connotations. A 16th century scholar editing a collection of Greek-language poetry wanted to come up with a word to distinguish the fact that they came from the later, Christian phase of the Greek-speaking world rather than the earlier, pagan period. Byzantine, after the original name of Constantinople, struck him as apposite for whatever reason, and later writers took that up as a label to describe the later, eastern, Christian, Greek-speaking phase of the Roman empire. But the relationship remains: Byzantium is a place, Byzantine is a word to describe stuff related to that place.

“Byzantium” was the original Greek name given to an important city in what is now Turkey. The Romans not only occupied it, but Emperor Constantine moved the capital of the Empire there… and even after Rome itself fell, Byzantium, renamed “Constantine” (City of Constantine), remained capital of the Eastern Roman Empire for another 1,000 years.

(As Edward Gibbon pointed out in his famous history, “The Decline and Fall of the Roman Empire,” the Roman Empire did not really fall with Rome itself but took another 1,000 years before Constantinople itself fell.)

Byzantium/Constantinople finally fell to the Ottoman Turks in 1453, just half a century before Columbus’ voyages.

At that point, the city did not disappear… on the contrary, It became the capital of the Turkish Ottoman Empire, and the Turks renamed it “Istanbul.”

However, THAT Empire finally fell during World War I, at which point the country became part of the modern nation of Turkey, which absorbed Istanbul. (Although the history of the nation reveals that the Old Empire was already in the process of dissolution anyway, replaced by the modern nationalist movement, which created the Turkey that exists today.)

As the historic capital of more than one great empire, Istanbul remains one of the great historical shrines in this world, and is one of the greatest destinations for tourism anywhere

.

Strictly speaking, Byzantium is the name of a city founded on the European side of the southern end of the Bosphorous, the strait connecting the Mediterranean and the Black Sea in the 7th century BC. In the early 4th century AD, the emperor Constantine selected the site as his capital, substantially rebuilding the city and renaming it Constantinople. Constantinople became the capital of the surviving eastern half of the empire once the line of western emperors ended in 476 AD. The eastern empire carried through many ups and downs until the city was conquered by the Ottomans in 1453, bringing it to an end. During most of that time (that is, from Constantine through the Ottomans) and even beyond, the name “Byzantium” was rarely used, and then only in a deliberately archaic and historical sense. However, in the late 1500s, a German scholar named Hieronymus Wolf editing a book of Christian Greek poetry decided he needed a distinctive name to describe the later, eastern, Christian, Greek-speaking phase of the empire, separate from the earlier, pan-Mediterranean, pagan, Latin-speaking phase, and he decided that Byzantium/Byzantine would do the trick. Since then, scholars have variously used “Byzantine” and “eastern Roman” to label that empire, with Byzantine becoming more popular over time. So, then, Byzantium-the-city was an ancient Greek city predating the empire and very nearly predating Rome itself, while Byzantium-the-empire was…well, complicated.

The Byzantine empire might be regarded as a successor state of the Roman empire, or perhaps a survivor of the empire. It was the eastern half of the empire which had already, because of a series of reforms under Diocletian, started acting in a semi-autonomous fashion and practically became its own independent entity when Rome proper fell. Complicating this in modern minds is the fact that the Byzantines considered themselves (legally and politically) Roman, but most were (ethnically) Greek as well. Greek was the language of art and commerce, and as time went by increasingly the language of law and government as well. But the modern nation-state didn’t exist yet, so they didn’t see themselves as different from earlier Romans because of language and location. They saw themselves as the legitimate holders of Roman tradition and legitimacy.

It was never called that by anyone until after the fall of Constantinople to the Ottoman Turks, the point at which historians started to become more interested in the history of the Byzantines in terms of being distinct from the earlier forms of the empire.

The term exists only for that reason ie we want to be able to easily differentiate between the Latin speaking, Pagan earlier period and the Greek speaking, Christian later period.

It is slightly deceptive in that it presents the two as different cultures, which isn’t the case at all. The Byzantines evolved from the earlier Romans in the same way that the empire evolved from the republic. The Romans were a continuous culture from around 750bce right through to 1453ce, it’s just that plenty changed over that time because culture is never static.

The east/west differentiation is also terminology that we are projecting back onto the Romans. They would not have recognised that distinction either, once again it’s to help us talk about the differences. To the people who lived in the era they would have been just “Romans” whether they lived in Rome, Britannia, Constantinople or wherever.

Yes. “Byzantine” was coined in the sixteenth century (by German legal scholar Hieronymus Wolf) to distinguish between the western empire, whose legal code he used as the basis of his work, and the eastern which he wanted to treat separately. It was originally a more-or-less neutral term to distinguish neatly between the Greek-language heritage of the east and the Latin-language heritage of the west, but almost from the start it developed negative connotations. Nowadays most English-speaking scholars use “East Roman” as a more neutral term.

In older contexts (typically before the year 330) “Byzantium” can also refer to the old Greek city of Byzantion, which was absorbed into Constantinople.

The same city has had THREE different names at different times:

1. Byzantium
2. Constantinople (just Byzantium renamed)
3. Istanbul.

This ancient city was originally named Byzantium. Then it was renamed in late antiquity to “Constantinople,” meaning, “the city of Constantine.”

It was the Roman Emperor Constantine who made that change and also:

1. Permanently moved the capital from Rome to Constantine.
2. Decreed freedom to be a Christian in the Empire, and by his example encouraged other converts.
3. Convened the Council of Nicea.

So he was a busy man.

Constantinople remained the capitol of what remained of the Roman Empire. This Eastern half that stood for another thousand years after Rome was sacked.

But the Ottoman Turks finally conquered Constantinople in 1453 and renamed it Istanbul.