Gold coins showing heads of Roman Emperors Constantine the Great and Diocletian, 4th century.

Gold coins showing heads of Roman Emperors Constantine the Great and Diocletian, 4th century. Constantine (c273-337) became emperor in 306. He rebuilt of the ancient Greek city of Byzantium, which was renamed Constantinople and became capital of the Roman Empire after his death. The reign of his predecessor Diocletian (245-313), which lasted from 284-305, saw the beginnings of the division of the Empire into two, eastern and western, halves, as well as a savage persecution of Christians. (Photo by Ann Ronan Pictures/Print Collector/Getty Images)