Olivier IV de Clisson, a great builder of castles, undertook the work with the aim of protecting the islanders in the event of foreign invasion. The longest of these had been led by the famous English pirate, Robert Knolles, who managed to seize the castle in 1355 and occupied the island for 37 years. In 1381, the île d'Yeu was retaken during the reconquest of Poitou by Olivier V de Clisson. The Vieux-château de l'Île d'Yeu has been classified as a Monument historique (Historic monument) since 1890.