340s

Roman Empire

• Constantinople, capital of Emperor Constantius II, becomes the largest city in the world, taking the lead from Rome, capital of his brother Constans I.^[1]
• Constantine II, Emperor of the central part of the Roman empire (the upper Danube, Italy and middle Africa), crosses the Alps and attacks the army of his brother Constans I, emperor of the western part of the Roman Empire (Britain, Gaul, the Rhine provinces and Iberia). They clash at Aquileia in northern Italy. Constantine is killed in a skirmish by an ambush of Constans' troops.
• Constans is left sole ruler of the Western Roman Empire, with his other brother, Constantius II, Emperor of the Eastern Roman Empire.

Religion

• Pope Julius I inveighs against Arianism at the Council of Rome.
• Acacius succeeds Eusebius as bishop in the see of Caesarea.
• Wulfila spreads evangelism among the Goths for 7 years.

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