Battle of Octodurus
56 BCE.
Shown on the map at 46.100°, 7.067°.
The battle of Octodurus took place in the winter of 57–56 BC in the Gallic town of Octodurus in what is now Martigny, Valais, Switzerland. The battle resulted from a Roman attempt to open the Great St. Bernard Pass over the Alps. It was a Roman victory, but the ferocity of the fighting ended with the Roman legion moving back out of the Alps.
Text from the Wikipedia article Battle of Octodurus, licensed CC BY-SA 4.0.