Byzantine Empire
The Byzantine Empire (or Byzantium) was the predominantly Greek-speaking remnant Eastern Roman Empire throughout Late Antiquity and the Middle Ages. Known simply as the Roman Empire (Greek: Βασιλεία Ῥωμαίων, Basileia Rhōmaiōn) or Romania (Ῥωμανία, Rhōmanía) by its contemporaries, the empire was centered on the capital of Byzantium (later renamed Constantinople under Emperor Constantine) and was ruled by emperors in direct succession to the ancient Roman Emperors after the collapse of the Western Roman Empire. The Empire was severely weakened in 1203 A.D. when Catholic crusaders sacked Constantinople. By 1511, the remnants of the Empire were still headed by the House of Palaeologos under Manuel Palaeologos.
The Byzantine Empire (technically speaking, the Roman Empire) ended in 1453 when the Ottomans led by Sultan Mehmet II conquered Constantinople.