Battle of the Save
388 CE.
Shown on the map at 46.419°, 15.871°.
The Battle of Poetovio was fought in 388 between the forces of Western Roman Emperor Magnus Maximus and the Eastern Roman Emperor Theodosius I. Magnus Maximus's army was defeated and Maximus was later captured and executed at Aquileia.
Text from the Wikipedia article Battle of Poetovio, licensed CC BY-SA 4.0.