The castellany of Fouras returned, in the 11th century, to the Rochefort family who obtained the rights to exercise high, medium and low justice, and to tax boats using the river (toll).
In 1305, Philippe le Bel bought Fouras and attached it to the crown, then again granted this fief which changed lords several times, until Jehan II de Brosse, lord of L'Aigle in 1449 (1454?), who built the keep from 1480 to 1490. This is the end of the Hundred Years' War.
During the wars of religion, the strategic position of Fouras allowed it to escape the destruction ordered by Louis XIII for all the strongholds after the capture of La Rochelle. He made it a royal fortress.
During the Dutch War (1672 to 1678), Fouras protected the Rochefort arsenal built in 1666 by defending the mouth of the Charente.
From 1689 to 1693, under the supervision of Vauban, François Ferry, engineer to Louis XIV, transformed the old feudal residence into a "sea fort". He thickened the walls of the keep and created, 36 m above the sea, a firing platform for 9 cannons. He strengthened the medieval rampart and reached out to the sea by building a false bray intended to carry the bulk of the cannons.
In 1705, Ferry had a barracks built on the current parking lot. It housed the garrison and served as a rampart for the keep.
The fort will be equipped with 50 cannons spread over 3 fire levels: the false braie, the courtyard and the top of the keep, and will have a garrison of 300 to 600 men. Its shape evokes that of a warship: the horseshoe structure at the front (bow), the upper medieval courtyard (upper deck), the keep (mast) and the ramparts (bridge)3.
The Fouras fort did not fire a shot, even during the two British attacks on the harbor, in 1757 and 1809. It was kept in service until the arsenal closed in 1927.
The fort and the citadel were classified as a historic monument on March 13, 1987.