In 1071, the sixth Count of Flanders, Arnulf III, was killed in the first Battle of Cassel by the forces of Robert the Frisian in a dispute over the succession to the title of count. Although Arnulf was numerically superior and was supported by King Philip I of France, Robert was able to defeat his rival's army and took the title of Count of Flanders with the acquiescence of Philip I after a further five years of struggle. The town was re-fortified, possibly by Robert, with a castle and a new set of walls built on the remains of the old Roman walls. The castle does not survive today – it was already in ruins by the early 18th century – but is depicted on old engravings as a large square tower, the "Tour Grise", dominating the western flank of the hill.