Fort Boyard is a fort located between the Île-d'Aix and the Île d'Oléron in the Pertuis d'Antioche straits, not far from La Rochelle.
It is 61 metres long, 31 metres wide, and its walls are 20 metres high.

The construction of the fort was first considered during a build-up of the French armed forces undertaken by Louis XIV between 1661 and 1667, but Vauban, his leading military engineer, famously advised against it, saying
"Sire, it would be easier to catch the moon with the teeth than take on such an endeavour in such a location".
Fort Boyard was to form a line of fortification with Fort Enet and Fort de la Rade on Île-d'Aix to protect the arsenal of Rochefort from Royal Navy incursions.