Château-Vieux, the medieval Old Castle of Bayonne, rises from the ruins of a Roman castrum established in antiquity to guard the confluence of the Nive and Adour rivers. Built by the Viscounts of Labourd in the late 11th century, its original hexagonal tower was enhanced by later medieval additions. The fortress underwent significant transformation in the 17th century under military engineer Vauban's fortification program and Governor Antoine de Gramont's direction, acquiring its present form with reinforced defenses. Though no longer open to the public—it now serves as the regimental headquarters of the 1st Marine Infantry Parachute Regiment—the castle remains an emblematic symbol of Bayonne's strategic importance in Basque Country.
