Battle of Llwchwr
1136 CE.
Shown on the map at 51.657°, -4.010°.
The Battle of Llwchwr (or Battle of Gower) was fought between Welsh and Norman forces between Loughor and Swansea on New Year's Day 1136.
Text from the Wikipedia article Battle of Llwchwr, licensed CC BY-SA 4.0.