the division between the Western Roman Empire and the Eastern Roman Empire. However, formally the Empire remained a single polity, with separate co-emperors in the separate courts. The fall of the Western Roman Empire is dated either from the de facto date of 476, when Romulus Augustulus was deposed by the Germanic Herulians led by Odoacer, or the de jure date of 480, on the death of Julius Nepos, when Eastern emperor Zeno ended recognition of a separate Western court. Historians typically refer to the empire in the centuries that followed as the "Byzantine Empire", orientated toward Hellenic culture and governed by the Byzantine emperors. Given that "Byzantine" is a later historiographical designation and the inhabitants and emperors of the empire continually maintained Roman identity, this designation is not used universally and continues to be a subject of specialist debate. Under Justinian I, in the sixth century, a large portion of the western empire was retaken, including Italy, Africa, and part of Spain. Over the course of the centuries thereafter, most of the imperial territories were lost, which eventually restricted the empire to Anatolia and the Balkans. The line of emperors continued until the death of Constantine XI Palaiologos at the fall of Constantinople in 1453, when the remaining territories were conquered by the Ottoman Turks led by Sultan Mehmed II. In the aftermath of the conquest, Mehmed II proclaimed himself kayser-i Rûm ("Caesar of the Romans"), thus claiming to be the new emperor, a claim maintained by succeeding sultans. Competing claims of succession to the Roman Empire have also been forwarded by various other states and empires, and by numerous later pretenders. Legitimacy While the imperial government of the Roman Empire was rarely called into question during its five centuries in the west and fifteen centuries in the east, individual emperors often faced unending challenges in the form of usurpation and perpetual civil wars. From the rise of Augustus, the first Roman emperor, in 27 BC to the sack of Rome in AD 455, there were over a hundred usurpations or attempted usurpations (an average of one usurpation or attempt about every four years). From the murder of Commodus in 192 until the fifth century, there was scarcely a single decade without succession conflicts and civil war. Very few emperors died of natural causes, with regicide in practical terms having become the expected end of a Roman emperor by