Château de Châtillon-d'Azergues, Medieval castle in Châtillon, France.

Château de Châtillon-d'Azergues is a ruined castle on a rocky spur above the village of Châtillon in the Rhône. Its polygonal enceinte, cut off by a deep dry ditch, encloses a 13th-century cylindrical keep 18.5 m high and 9.5 m in diameter with 1.5 m thick walls, and a 12th-century rectangular building with flat buttresses linked by blind arcades in a Lombardy frieze. A small square structure beside the east gate retains a vaulted ground floor and a 14th-century oratory.

The castle is first documented in 1173, when the Count of Forez ceded it to the Archbishop of Lyon. In the 13th century it passed from the Oingt family to the Albons by marriage, and a 1260 act records the keep as the lord's private retreat. Rebuilt between 1418 and 1464 by Jean Jossard, it was bought in 1882 by Antoine Biolay and listed as a monument historique in 1937.

The Chapel of Saint-Barthélémy, also called Notre-Dame-de-Bon-Secours, stands east of the castle and was its original chapel. It was listed as a monument historique in 1862, before the castle ruins were listed in 1937. Geoffray de Balsac restored and enlarged it and was buried there in 1510.

The castle is privately owned and closed to the public; the Chapel of Saint-Barthélémy, listed in 1862, stands beside it. The ruins occupy the southern tip of a rocky spur at the top of the village, near the church, and are reached by a narrow passage between the chapel and the castle walls. Restoration work was carried out between 1934 and 1960.

The keep is an impressive cylindrical structure that rises over several stories and represents medieval defensive technology of its era. Its form and height allowed inhabitants to maintain a commanding view of the surrounding landscape.