The Château-Vieux, or Old Castle, is the oldest substantial structure in Bayonne, its origins going back to a Roman castellum. The core of the current building dates from the 12th century, when Bayonne was under English Plantagenet rule — one of the more curious footnotes of medieval history, this corner of the Basque coast belonged to England for three centuries. The castle changed hands repeatedly between English and French rule, and was substantially modified under each.
Today the castle is largely closed to the public and occupied by the army, but the exterior and ramparts are well worth seeing. The square tower and the riverside façade give a good sense of the medieval fortifications that once defended the confluence of the Adour and Nive. The nearby Vauban-designed ramparts, built under Louis XIV, can be walked and form a pleasant circuit around the old town.