Gravelines (Dutch:Grevelingen) is a commune in the Nord department in Northern France. It lies at the mouth of the river Aa 15 miles (24 km) southwest of Dunkirk. It was formed in the 12th century around the mouth of a canal built to connect Saint-Omer with the sea. As it was on the western borders of Spanish territory in Flanders it became heavily fortified, some of which still remains.