The British landing on the beaches of Rivedoux in July 1627 (10.000 soldiers commanded by the Duke of Buckingham) had shown the weaknesses in the coastal defences of the Ile de Ré and the coasts of Aunis and Saintonge.
In 1672, Colbert, Secretary of the Navy became aware of the vulnerability of France's western islands and the new military port of Rochefort. The military engineer Vauban was entrusted to organize the defence of the Islands and the estuary of the Charente. He proposed the construction of three forts on the Island, including that of Sablanceaux in 1674.
A 45 metre square, the building is located in the middle of a large gently sloping moat, a deep dry ditch with two shoulders on the right and the left which block off the Isthmus of Sablanceaux.
A single entry with a drawbridge opens to the west towards the village.
The parapet wall has openings for guns whose line of fire was directed towards the point and the beaches of north and south Rivedoux.
A long entrance corridor whose length shows the the thickness of the wall opens onto a small courtyard surrounded by two guard houses (latrines and 3 living rooms with fireplaces), drinking water wells and two powder magazines, one on the ground floor and one dug underground beneath the wall.