The Byzantine Empire is the term casually used since the 19th century to describe the Eastern Roman Empire which was centered on its capital, Constantinople. During much of its history it was known to many of its Western contemporaries as the Empire of the Greeks because of the predominance of Greek language, culture and population. To its inhabitants, the Empire was simply the Roman Empire (Greek: Βασιλεία Ῥωμαίων), and its emperors continued the unbroken succession of Roman emperors. In the later Islamic world it was known primarily as روم (Rûm, land of the "Romans").
Byzantium had been a modest Greek settlement at the furthest extremity of the European continent, on the Sea of Marmara, and said to have been founded in 658 BC, by a group of colonists from the Greek city of Magara. The Emperor Constantine I, "The Great" (reigned AD 306–337), is generally considered to be the first 'Byzantine' Emperor. It was he who decided, towards the end of 324, some six months or so before the Council of Nicaea, which he opened, to move the Imperial capital from a tottering Rome to Byzantium, refounded and renamed it Constantinople, or the Nova Roma (New Rome). The formal ceremony founding the new city was 4th November 328, and construction work on the new city and its walls began "at a furious rate". He was baptised by his own request into the Christian faith, licensed it throughout the Roman Empire and made it the State religion. The Church in Council met and the Patriarchs bestowed upon the Emperor his semi-holy status as "Divine Head of the Church" and "God's Viceroy on Earth". The period after Constantine's death again saw some persecutions of Christians but the Emperor Theodosius I (379–395) ordered that this be halted and that Christianity finally supplant the old pagan Roman religions. Following his death in 395, the political division between East and West became permanent. Some writers place the real commencement of the Eastern Empire yet later, in 476, when Romulus Augustulus, traditionally considered the last western Emperor, was deposed, thus leaving sole Imperial authority with the emperor in the East. Some even point to the reorganization of the empire in the time of the Emperor Heraclius (circa 620), when Latin titles and usages were officially replaced with Greek versions. In any case, the changeover was gradual but permanent and when Constantine inaugurated his new capital, the process of Hellenization and increasing Christianization was already under way.
The Empire is generally considered to have ended after the fall of Constantinople to the Ottoman Turks after a great siege in 1453, although 'Greek' rule continued over fragments of the Empire's territory for several more years, until the fall of Mystras in 1460, Trebizond in 1461, and Monemvasia in 1471.
- Norwich, John Julius, Byzantium, London, 1988, republished by the Folio Society 2003: vol.1, "The Early Years, vol.2, "The Apogee", vol.3, "The Decline and Fall".