350–353 Late period The Battle of Adrianople was fought in Thrace on July 3, 324,[2] during a Roman civil war, the second to be waged between the two emperors Constantine I and Licinius.

Constantine built up military momentum, winning further battles on land and sea, eventually leading to the final defeat of Licinius at Chrysopolis.

Constantine had, in a previous war (in 316), defeated Licinius at the Battle of Cibalae and conquered from him the entire Balkan Peninsula, with the exception of Thrace and Lower Moesia.

By 324 Constantine was ready to renew the conflict, and when his army, in pursuit of a raiding force of Visigoths, or possibly Sarmatians, crossed into Licinius' territory, an opportune casus belli was created.

Constantine invaded Thrace in force; his army was smaller than that of Licinius, but it contained many battle-hardened veterans and, as he had control of the Illyrian region, the finest-quality new recruits.

Licinius arranged his defensive line, of 200 stades in length,[5] in a strong position between a height overlooking the town and the confluence of the Hebrus with a tributary.

At this point in the campaign, control of the narrow waters separating Thrace and Asia Minor became of the utmost importance to both emperors.

[13] Initially, yielding to the pleas of his sister, Constantine spared the life of his brother-in-law, but some months later he ordered his execution, thereby breaking his solemn oath.