The Byzantine Empire was the significant remnant of the Roman Empire that survived in southeastern Europe for a thousand years after the official fall of Rome in 476 CE. As noted, a key difference with Rome was that the Byzantine Empire was always Christian rather than pagan. This hardwired into Byzantium a lack of cultural openness to the kind of religious diversity that had helped classical Rome to expand and thrive.

Another important difference was the relative weakness of Byzantium vis-à-vis the Roman Republic's power in its heyday. While powerful in some ways, Byzantium did not function as a hegemonic cultural, political, and military superpower in the same way as did the classical Roman Empire. This had the downside of leaving western Europe vulnerable to attacks, particularly from Viking marauders, that would not have occurred under the Roman Empire, but this also created an upside in which the western Europeans were forced to create their own vibrant and flexible cultural, political, and military institutions and infrastructures in order to survive.

Byzantium remained crucially important, however, because it controlled Constantinople, the gateway to the Mediterranean as well the gateway to overland passages to Asia. This was a source of access to vital trade routes with the East that this remnant of the Roman empire safeguarded for western Europe. Unfortunately, however, unlike Rome in its heyday, Byzantium ultimately lacked military might to keep this territory from Muslim conquest.

The Byzantine Empire was, in a sense, the continuation of the Roman Empire. It is even sometimes called the eastern Roman Empire, it included the Greek speaking eastern part of the Mediterranean. The Byzantine Empire was a Christian one and it was known for warring with the Muslims. It was a flourishing empire during the reign of the Macedonian emperors and its demise resulted as a consequence of attacks from Crusaders and Turks. Byzantium was a small but important town, it acted as a frontier between the Persian and Greek world. Both would become a part of Alexander the Great’s hellenistic universe during the fourth century BCE. The approach of the third century CE saw the Roman Empire with thousands of miles of borders to defend. It was the Emperor Constantine that realized that the problems of empire could not be managed from great distances. The Emperor Constantine renamed Byzantium after himself, Constantinople, and in 330 CE he moved there making it his new permanent restaurant. Constantinople was halfway between the Euphrates and the Balkan, and was not very far from the wealth of Asia Minor which at the time was a major part of the empire. After Constantine died the Roman empire divided into eastern and western sections. The Western Roman Empire ended by 476 CE when the last ruler got dethroned and a military leader took power. The Roman Empire during the fourth century became increasingly Christian, and the Byzantine Empire was definitely Christian. It was the first empire that was not just founded on worldly power, but on the authority of the Christian Church. During the first few centuries of the Byzantine Empire polytheistic religions stuck around as an important source of inspiration. Once Christianity got organized the Church had five leading patriarchs who lived in Antioch, Alexandria, Constantinople, Jerusalem, and Rome. In 451 CE the patriarch of Constantinople was named the second authority in ecclesiastical hierarchy, only the Pope in Rome was superior. The Great Schism of 1054 CE resulted in the eastern or Orthodox church(Byzantine) separating form the western church (Roman Catholic). Some basic comparisons between the two empires were the reasons for the end of the empires. The Byzantine Empire ended due to conquest where the Roman Empire ended because it was incorporated into a New Entity. Both of the Empires has the same form of government, Authoritarian, also both were ruled by hereditary rulers. The empires had differing main languages, in the Roman Empire they mainly spoke latin and in the Byzantine Empire the most common language was Greek. In the Roman Empire, until the reign of Constantine I, the main religion was polytheistic where they worshiped the various renamed Greek gods. Emperor Constantine I’s reign was when Christianity became the main religion of the empire. The Byzantine Empire was a Christian one from the start. The Roman Empire, before its division, covered a larger geographical area that the Byzantine Empire ever did.

What distinguishes the Byzantine Empire from the Roman Empire?

The Byzantine Empire is distinguished from the Roman Empire largely by geography, culture, and religion.

The Byzantine Empire had its origins in the Roman Empire.  Beginning in the 300s AD, Constantinople essentially became the capital of the Roman Empire in the East.  This split with Rome became official in 395.  At that point, it was still the Eastern Roman Empire, not the Byzantine Empire.

The Byzantine Empire came to differ from the Roman or Western Roman Empire in a number of ways.  Geographically, it was centered in the East, with the capital in Constantinople which is in what is now Turkey.  The Byzantines did briefly conquer and control Italy, but for the most part, this was an eastern empire.  Culturally, the Byzantine Empire was Greek, not Roman, with Latin eventually falling out of use completely.  In terms of religion, it was built as a Christian empire from its beginnings, instead of being an empire built on pagan foundations as the West was.

All of these are ways in which the two empires are distinct even though the one gave rise to the other.