The Tour Harold is a stout circular tower built into the medieval ramparts of the upper town, dating in its present form to the late thirteenth or early fourteenth century. The name comes from the persistent local tradition that this is where Harold Godwinson was held captive by Count Guy of Ponthieu after being shipwrecked on the Picardy coast — the historical site of the imprisonment is more usually placed at Beaurain inland, but the story has attached itself firmly to the tower here.
Whatever the truth of the legend, the tower itself is the best surviving piece of military architecture in St-Valéry. The walls are several metres thick at the base, with narrow arrow slits and a flat top that once carried a wooden hoarding. The tower is not normally open to the public, but its exterior is visible from the rampart walk.