Galerius, was the partner of Diocletian in the Tetrarchic system of government, where the empire was ruled by two senior emperors, one in the east and one in the west, each with a junior to assist them. He repelled a Persian invasion in the east and with his counteroffensive pushed the invaders back, sacking Ctesiphon itself and securing a very favorable peace for Rome. Like Diocletian he was initially committed to persecuting his Christian subjects, but eventually came around, passing an Edict of Toleration 311 CE, two years before the more famous edict of Constantine the Great.