324 AD

Constantine I becomes sole Roman Emperor

A period of civil war concludes with Constantine I as sole emperor of the eastern and western Roman Empire. He commences construction of New Rome (Constantinople) on the site of the old Greek city of Byzantium.

Constantine instigates a series of legislative changes that favour Christians within the Roman Empire.

325

The Council of Nicaea

Constantine is not prepared to tolerate divisions within the Christian Church, a threat to Roman stability that he regards as "formidable as any war or battle". An ecumenical ("world –wide") council of church leaders is convened at Nicaea to debate Arianism; a popular religious doctrine, which holds that Jesus Christ ("the Son"), is inferior to God ("the Father").

The Council counters Arianism with the Nicene Creed, a theological formulation which includes the statement that the Son and Father are of the same substance and therefore equal.

Although the Council apparently 'solves' the problem of Arianism, the heresy continues to exist and gain many adherents over the next two centuries, including some of Constantine’s successors.

330

Constantinople formally dedicated as Roman Capital

330 is often treated as a convenient starting point for referring to the Roman Empire in the East as the "Byzantine Empire" or "Byzantium".

410

Rome is sacked by Alaric the Visigoth

Although Rome, as a capital city, had long ceased to have any real significance in practical terms, its fall to a tribe of barbarians marks the irrevocable decline of the Roman Empire in the West. Western Roman Emperors continue to be appointed for the next sixty years, but they have little real standing.

413

Construction of Constantinople’s triple walls begin

Although commonly known as the "Theodosian Walls" after Theodosios II, the reigning emperor), the walls were actually built on the orders of Anthemius, the Empire’s Prefect of the East, to counter an immediate threat from the Huns.

In conjunction with Constantinople's naturally strong location, the Theodosian walls will prove their worth against any number of attacks upon Constantinople through Byzantine history. They will fall to an attacking army only twice, once during the chaos of the Fourth Crusade (1204) and, finally, to the Ottoman Turks, who breach them in 1453 with the help of artillery and overwhelming numbers.

455

Rome is sacked for the second time.

This time, in a very systematic and controlled manner, by the Vandals – another tribe of Germanic barbarians. The Vandals go on to establish a kingdom in the Roman provinces of North Africa, whilst the Goths establish themselves in Italy and Spain.

476

Formal end of the Roman Empire in the West.

The last Western Emperor, Romulus Augustulus, is deposed.