When, a few years later, Diocletian abruptly retired as emperor, he made the fateful decision to divide the Empire into a tetrarchy ruled by two sets of junior and senior emperors, one in the east and one in the west. It was an untenable situation that quickly devolved into civil war between rival claimants to the throne. In 312 C.E., one of these claimants rode with his army to the River Tiber in an attempt to reinstitute the rule of a single emperor. His name was Constantine, and he would alter the course of both Rome and Christianity forever.
