The greatest of medieval civilizations was the Eastern Roman Empire. The Roman Empire was divided in 395. The Western half, ruled from Rome, was ruled by the barbarians in the 5th century. The Eastern half, known as the Byzantine Empire, lasted for more than over 1,000 years. The Byzantine Empire was one of the leading civilizations in the world. In 324, Constantine, the first Christian emperor, became the single ruler of the Roman Empire. He set up his Eastern headquarters at the ancient Greek colony of Byzantium in 330. This city, later renamed Constantinople, was also known as "new Rome." It became the capital of the Byzantines after the Roman Empire was divided. Constantinople was located on the European shore of the Bosporus, between the Aegean and Black seas, in what is now the countryside of Turkey. The city brought together people from Europe and Asia. During the ten and a half centuries that the Byzantine Empire lasted, its boundaries continually changed. The territory that made up the empire in 565 included Italy, Sicily, North Africa, southern Spain and Syria. At its largest during 1000, the Byzantine Empire included Greece, Italy, Egypt, Syria, North Africa, and southern Spain. The first era of Byzantine civilization lasted from about 324 to 640. During this time, the separate identity of the empire was established. The first great period of the Byzantines occurred during the reign of Justinian I, who took the throne in 527. Justinian had reconquered much of the territory that had fallen into barbarian hands. He also built Constantinople into one of the most magnificent cities of the world. There was much conflict during the first years of the Byzantine empire. Barbarian people, eager for land and power, pushed at its boundaries during the 5th century. At first, the Byzantines attempted to form an uneasy peace with the barbarians who surrounded them. Justinian I became emperor in 527, and ruled until 565.