|Colbert, the naval minister of Louis XIV decided in 1666 to build a major naval shipyard and arsenal in Rochefort, leading to a complete overhaul of the coastal fortifications of the Aunis county.|
Among these fortifications, it was decided to build a fort at the headland of the Chapus near the village of Bourcefranc. This fort had the task of preventing any naval circumvallation of the citadel of the Chateau d’Oleron by ensuring protection of the south against hostile British or Dutch frigates or even ships of the line which could have sneaked through the difficult Maumusson strait.
The Vauban's project, which was executed by Ferry, was a half circular horse shoe shape fort with two pier-heads with one low level battery and a tower-reduit at the gorge. The fort access to mainland was ensured by a causeway submersible at high tide.