Cassel is a commune in the Nord department in northern France. Built on a prominent hill overlooking French Flanders, the town has existed since Roman times. It was developed by the Romans into an important urban centre and was the focus of a network of roads, which are still in use today, that converge on the hill. After the fall of the Roman Empire, Cassel became an important fortified stronghold for the rulers of Flanders which was repeatedly fought over before finally being annexed to France in the 17th century. It was the headquarters of Marshal Ferdinand Foch during part of the First World War. In 1940, during the German invasion of France, Cassel was the scene of a fierce three-day battle between British forces and German forces which resulted in much of the town being destroyed.