Battle of the Boarn
734 CE.
Shown on the map at 53.077°, 5.794°.
The Battle of the Boarn (West Frisian: Slach oan de Boarn; Dutch: Slag aan de Boorne) or Battle by Jirnsum was an 8th century battle between the Franks and the Frisians near the mouth of the river Boarn in what is now Jirnsum in the Dutch province of Friesland.
Text from the Wikipedia article Battle of the Boarn, licensed CC BY-SA 4.0.