Château de Blanquefort, Medieval castle in Blanquefort, France.

Château de Blanquefort is a ruined fortress 1 km south of Blanquefort, in Gironde. Its oldest part is an 11th-century rectangular Romanesque keep of small rubble stone, 18 by 11 metres. At the end of the 13th century six round towers were added, forming a continuous wall-walk, and a stone enceinte replaced the wooden palisade. Two broken round towers and a jagged wall fragment remain.

A stone keep was built in the 11th century, making it the oldest attested stone castle in Gironde. The Blanquefort family died out around 1250, and the kings of England bought the castle in 1254 and 1270. Edward II ceded the lordship in June 1308 to Bertrand II de Got, nephew of Pope Clement V; it passed by inheritance in 1325 to Aymeri de Durfort. After the Fronde, Mazarin had the battlements razed, and the castle was abandoned after a fire in the second half of the 17th century.

The fortress reflects medieval military design through its combination of early stone foundations and towers that were later modified to defend against cannons. Visitors can trace these different building phases by observing the varied stonework and structural elements throughout the site.

The ruins can be viewed from outside along the surrounding grounds, with access available via Rue de la Forteresse in the town center. It is advisable to check ahead for current conditions or any access restrictions before visiting.

The castle's name, and that of the town, comes from "Blanqua fortis", the white fort, likely for the pale limestone walls rising from the marshes when even churches were still built of wood. Excavations also found Roman tegulae in the foundations and two coins of Constantine the Great.