Battle of the Hellespont
324 CE.
Shown on the map at 40.200°, 26.400°.
The Battle of the Hellespont, consisting of two separate naval clashes, was fought in 324 between a Constantinian fleet, led by the eldest son of Constantine I, Crispus; and a larger fleet under Licinius' admiral, Abantus (or Amandus). Despite being outnumbered, Crispus won a very complete victory.
Text from the Wikipedia article Battle of the Hellespont, licensed CC BY-SA 4.0.