Constantine the Great

Gaius Flavius Valerius Constantinus was born in the early 270s at Naissus (now Niš). His father Constantius Chlorus rose to western augustus under Diocletian's tetrarchy; his mother Helena, an innkeeper's daughter from Bithynia, was set aside for political reasons but later venerated as Saint Helena.

When Constantius died at York in July 306, the legions acclaimed Constantine augustus on the spot — an irregular act that triggered nearly two decades of civil war. He pressured Maximian to suicide in 310 and crushed Maxentius at the Milvian Bridge in October 312, allegedly after a vision of the chi-rho. In 313 he and Licinius granted religious freedom to Christians and all others at Milan. After defeating Licinius in 324 he became sole emperor.

The reforms were sweeping. The solidus became the Mediterranean's reserve currency for a millennium. He split civil and military authority, disbanded the Praetorian Guard and rebuilt the army around mobile comitatenses and frontier limitanei. He tied coloni to their estates, a distant ancestor of serfdom. On 11 May 330 he turned Byzantion into Constantinople, capital of the Eastern Empire for over a thousand years.

In religion, he summoned the first ecumenical council, Nicaea I, in 325. It condemned Arianism and produced the Nicene Creed — the first time imperial power brokered Christian doctrine. He styled himself bishop of those outside the church and was baptised only on his deathbed.

The shadow is real. In 326 he executed his eldest son Crispus and his wife Fausta; the sources are deliberately vague, but the erasure of both names from inscriptions confirms a major scandal. He left the empire divided among three quarrelling sons.

He died on 22 May 337 outside Nicomedia and was buried among the apostles. Christianity legalised, the new capital and the solidus on one side, the dynastic killings on the other — together they make him the bridge between classical Rome and the medieval Christian world.