The Byzantine Empire The Byzantine Empire, the survivor of the Roman empire, flourished into the oldest and longest lasting empire in our history. It began with Constantine the Great's triumph of Christianity. He then transferred his capital from Rome to the refounded Byzantium in the early 4th century, year 330 AD, and named it Constantinople after himself. This city became the surviving safe spot after the breakup of the Western Roman empire by the 5th century. It was by far the largest and richest city in Christendom during the Middle Ages with a population of about one million people. (Encarta) Constantine