In 306 Constantius I Chlorus, formerly a caesar, was co-emperor ruling the West. He and his son Constantine crossed to Britain and drove back an invasion by the untamed tribes north of Hadrian’s Wall. When Constantius died suddenly at York, Constantine was hailed as emperor by his troops and became a caesar, controlling Gaul and Britain, in a reconstituted Tetrarchy. Six years of military and political intrigues followed until in 312 Constantine was strong enough to invade Italy, defeat his rival Maxentius at the Milvian Bridge, and became emperor the West. Before the battle he is said to have looked at the sky and seen a cross and the legend in hoc signo vinces : In this sign, conquer. Whether or not this actually happened, Constantine favoured Christianity from at least this time, by contrast with earlier emperors who had looked to the old Roman religion to restore the old Roman virtues. By the edict of Milan 313, Constantine and the emperor in the East, Licinius, proclaimed general toleration and the restoration of confiscated Christian property. Later Licinius began to persecute Christians, perhaps because the new faith had become politically indentified with Constantine. War broke out, Licinius was defeated and by 324 Constantine was master of re-united Roman world.
Christians were far more numerous in the East, and Constantine could now safely lavish patronage on the church. Having long made way against imperial indifference or active hostility, Christianity flourished throughout Constantine’s reign, no doubt gaining strenght as doubters realized that it did not involve un-Roman weaknesses such as pacifism. One of Constantine’s earliest actions as a ruler of the Roman world was to convene an ecumenical council at Nicaea in Bithynia 325, which attempted to resolve the conflict between those who believed Jesus and God were of one subtance and those who believed they were separate. The Arian heresy, as the victors later called it, despite the orthodox victory at Nicaea, Arianism was to play an important part in the later history of the Empire. By the end of Constantine’s reign Christianity was effectively the state religion, althought it was not as yet persecuting its rivals.
Constantine’s greatest material legacy was a new capital, begun in 326 and dedicated in 330 on the site of the old Greek city of Byzantium. New Rome, which was soon to become known as Constantinople, “the city of Constantine” was planned as a Christian capital althought pagan as well as Christian ceremonies were discreetly allowed at its foundation, no pagan temples were built within its walls. The site was superbly chosen. The end of a small peninsula on the European coast of the Bosporus where it joins the Sea of Marmara. Surrounded on three sides by the sea, it became near-impregnable when immenselystrong walls were built across the peninsula: indedtations in the coastline provided good harbours, and a long inlet, the Golden Horn, was large enough to shelter a navy but narrow enough for for defenders to keep out enemy ships by stringing chains across the entrance. The city controlled the natural land route from Europe to Asia and the sea route from the Mediterranean into the Black sea, and it served as a well-placed headquarters for an Empire apparently most strongly menaced from across the Danube and the Tigris. Constatine’s choise, not so very far from Nicomedia, confirmed Diolectian’s wisdom in making the East the new heart of the Empire, and Constantinople would be a Christian imperial city for the next eleven hundred years.
In many other respects Constantine furthered Diolectian’s work. The imperial bureaucracy grew still larger and was equipped with everwider powers and duties, the separation between civil and military powers became complete, the admission of barbarians as army recruits continued. Taxation remained onerous, and measures were taken to prevent peasants from leaving the land and the wealthy from evading municipal office. The attempt to create a rigid but stable society had some success for althought the value of the old silver denarius continued to depreciate there was at least a partial economic recovery, mainly thanks to the introduction of a new coin, the gold solidus. And by favouring the new Christian faith Constantine promoted an ideology that was to prove effective in increasing sosial cohesion and would long outlive the Empire and the world of late antiquity.
Source : Nathaniel Harris : History of Ancient Rome, 2000