Saint-Clair-sur-Epte is a commune in the Val-d'Oise department in Île-de-France in northern France.
The treaty of Saint-Clair-sur-Epte in 911 established Rollo, a Norse warlord and Viking leader, as the first Duke of Normandy.
Henry I of England seized the castle of Saint-Clair-sur-Epte in 1118.
Wikipedia https://en.wikipedia.org/wiki/Saint-Clair-sur-Epte
Coordinates 49°12'23.002" N 1°40'44.278" E
