Tour de l'Isleau, Tower in Saint-Sulpice-d'Arnoult, Charente-Maritime, France

Tour de l'Isleau is a square stone keep measuring 11 metres on each side and rising 17 metres to its terrace, set on a small hill above marshland. Its light grey squared-stone facade is divided into three bays by four vertical buttresses running the full height, with a single small rectangular window in the right bay. A quadrangular enclosure with small corner towers once surrounded it.

The keep dates from the 12th century and is among the oldest military monuments in the region; some attribute its building to Henry III Plantagenet, though the first lord known with certainty is knight Pont de Vivonne, named in a 1368 aveu sealed at his chastellery of Lileau near Pontlabay. In 1521 Jean III Isle de la Cave inherited it from his uncle Guy d'Estuer, and it passed to François Isle de la Matassière in 1557, then Daniel Isle de Forgette in 1578. The barons de la Chaume owned the domain in the 17th and 18th centuries; abandoned to brambles in the 19th century, it has been restored by private owners since 1974 and was inscribed as a monument historique on 14 May 1925.

The name Isleau comes from the old French "Lileau", meaning "the little island", a reference to the hill rising above the marsh. The tower was the seat of a castellany, and a 1368 charter sealed by Pont de Vivonne calls it "chastellerie de Lileau près de Pontlabay". Nearby are the remains of a modest chapel from a former village that stood on the hill.

The tower stands near the road from Saint-Sulpice-d'Arnoult to Corme-Royal, on a small rise above the marsh. It is a private property, so visitors view the keep and the remains of its quadrangular enclosure from outside. The site was inscribed as a monument historique on 14 May 1925.

The keep was already in ruins by the 19th century, when it belonged to farmers and was overgrown with brambles and weeds. Private owners began restoring it in 1974. The square enclosure with its small corner towers, still standing in the 19th century, has since disappeared.