Citadelle Vauban.

The fortifications of Belle île were developed and erected by the military architect Vauban
(Sébastien Le Prestre de Vauban, 1633-1707) on behalf of Nicolas Fouquet, marquis de Belle-Île,
prior to Fouquet falling out of favor with of King Louis XIV, probably because of his
extravagant displays of wealth (the king had Fouquet imprisoned from 1661 until his death in 1680).

The restored citadel is now a museum and hotel.