The Roman Empire ( ; ) was the post-Republican period of ancient Rome. As a polity, it included large territorial holdings around the Mediterranean Sea in Europe, North Africa, and Western Asia, and was ruled by emperors. From the accession of Caesar Augustus as the first Roman emperor to the military anarchy of the 3rd century, it was a Principate with Italia as the metropole of its provinces and the city of Rome as its sole capital. The Empire was later ruled by multiple emperors who shared control over the Western Roman Empire and the Eastern Roman Empire. The city of Rome remained the nominal capital of both parts until AD 476 when the imperial insignia were sent to Constantinople following the capture of the Western capital of Ravenna by the Germanic barbarians. The adoption of Christianity as the state church of the Roman Empire in AD 380 and the fall of the Western Roman Empire to Germanic kings conventionally marks the end of classical antiquity and the beginning of the Middle Ages. Because of these events, along with the gradual Hellenization of the Eastern Roman Empire, historians distinguish the medieval Roman Empire that remained in the Eastern provinces as the Byzantine Empire. The predecessor state of the Roman Empire, the Roman Republic, became severely destabilized in civil wars and political conflicts. In the middle of the 1st century BC, Julius Caesar was appointed as dictator perpetuo ("dictator in perpetuity"), and then assassinated in 44 BC. Civil wars and proscriptions continued, eventually culminating in the victory of Octavian over Mark Antony and Cleopatra at the Battle of Actium in 31 BC. The following year, Octavian conquered the Ptolemaic Kingdom in Egypt, ending the Hellenistic period that had begun with the 4th century BC conquests of Alexander the Great. Octavian's power became unassailable and the Roman Senate granted him overarching power and the new title of Augustus, making him the first Roman emperor. The vast Roman territories were organized in senatorial and imperial provinces except Italy, which continued to serve as a metropole. The first two centuries of the Roman Empire saw a period of unprecedented stability and prosperity known as the Pax Romana (). Rome reached its greatest territorial expanse during the reign of Trajan (AD 98–117); a period of increasing trouble and decline began with the reign of Commodus (177–192). In the 3rd century, the Empire underwent a crisis