The Byzantine Empire emerged as the Eastern Roman Empire after Constantine renamed Byzantium as Constantinople in 330. It controlled important trade routes between Europe and Asia. Justinian was a notable Byzantine emperor from 527-565 who had Roman laws collected and organized, influencing laws in Western Europe. The Byzantine Empire preserved Roman heritage and split from the Western church, using Greek and allowing clergy to marry. Kiev emerged as a center of Russian state in the 9th century after Slavs migrated south. Mongol rule in the 13th century isolated Russia but also influenced the tradition of absolute rule that later Russian tsars would wield.