Constantine I ruled the Roman Empire as Emperor from 306 to 337. He managed the unlikely task of both centralizing the Roman Empire and setting the stage for its ultimate fragmentation.

First came centralization, remedying a political nightmare created in 293 by a predecessor, Emperor Diocletian. Diocletian had divided the Empire into four administrative units, with himself retaining direct rule of the two eastern units from a capital at Nicomedia in present-day Turkey while delegating rule of the two western units to a subordinate based in Italy. Diocletian died in 306 and by the following year, when Constantine succeeded his father as ruler of the western provinces, the system had already spawned no fewer than seven claimants to Diocletian's throne. Constantine, however, managed to unite the Empire through a series of military successes culminating in defeat of his principal western rival Maxentius at the Battle of Milvian Bridge in 312.

Yet although Constantine had unified the Empire under a single ruler, the same military and political expediencies that had led Diocletian to seek a capital in the east finally led Constantine to the same result. In 330 he removed his capital to Byzantium, which was renamed Constantinople--a name it retained until the 20th century, when it became Istanbul. Although Constantine avoided the mistake of Diocletian in placing the western sector of the Empire under rule of a potential rival, the geographical span of the Empire created an inherent instability that was to result in a conclusive division of the Empire into two parts just 65 years later.

In fact, Constantine's greatest impact upon history was neither his reunification of the Empire nor his contribution toward its final division. History remembers Constantine for his Edict of Milan in 313, which removed the legal ban on Christianity within the Empire. Constantine attributed his victory at the Battle of Milvian Bridge to his having fought it under the sign of Christ--because of a dream on the eve of battle.