BYZANTIUM OR BYZANTINE EMPIRE
Conventional name of a medieval state that existed for more than one thousand years.
It can be viewed as a continuation of the Roman Empire inasmuch as its legal and administrative systems retained numerous Roman features; at the same time, it underwent significant transformations, evolving into a Christian and primarily Greek-speaking state centered on the Balkans and eastern Mediterranean.
The Byzantines themselves called their state the Roman Empire ('basileia ton Rhomaion') rather than Byzantium, applying the name Byzantion only to their capital, renamed Constantinople. Byzantium as a term for the state was introduced into scholarship only in the 16th century by Hieronymus Wolf (1516-80).
Since there is no act formally proclaiming the inauguration of Byzantium, no revolution abolishing the "ancient regime," the date of its beginning remains under discussion; most scholars prefer the date of 324 (or 330), when Constantinople was founded by Constantine I the Great, or 395, when the Roman Empire was divided between the sons of Theodosios I.
It is easier to set a precise date for the end of Byzantium; it ceased to exist in 1453 when Constantinople was captured by the Ottomans, although some remnants of the empire (the despotate of Morea, the empire of Trebizond) retained their independence until 1460 and 1461 respectively.
<Excerpt from the lengthy entry on 'Byzantium' (ODB'91, vol.1, p.344)>