Château Guillaume de Lignac, Medieval castle in Lignac, France

Château Guillaume stands in the Allemette valley in Lignac, in the Indre department. Its keep dates from the 12th century; in the 14th century four large cylindrical towers were built around it and the keep was crowned with machicolations. A pale stone model shows the square tower, the central round tower with its conical roof and crenellated parapet, and a gatehouse with a smaller turret.

According to the comte de Beauchamp's study, the castle was begun around 1103 by William IX of Aquitaine, the 'troubadour duke', after his return from crusade, and continued by his son William X, father of Eleanor of Aquitaine. The keep dates from the 12th century; in the 14th century it was flanked by four cylindrical towers and crowned with machicolations. Dismantled under Richelieu, it was restored by Charles Cazaux, a disciple of Viollet-le-Duc, between 1879 and 1883.

The name Château-Guillaume comes from a supposed founder, William IX of Aquitaine, the 'troubadour duke' and patron of courtly love. During the French Revolution the commune took the name Guillaume-Tell. In 1526 Jacqueline de La Trémoïlle brought the castle to Claude Gouffier, who had the keep and the Tour de La Trémouille roofed and fitted out a new apartment.

The castle stands in the Allemette valley, a small river of the Anglin valley, in the hamlet of Château-Guillaume, now part of Lignac in the Indre. The site is a classified monument; the surviving keep and its four cylindrical towers are best read from outside, where the 14th-century machicolations and the 1879–1883 restoration by Charles Cazaux can be seen.

The castle stands in the Allemette valley, a small river of the Anglin valley. During the French Revolution the former commune of Château-Guillaume was renamed Guillaume-Tell, and in 1819 it was merged into Lignac. The name itself is attributed to William IX of Aquitaine, the troubadour duke, said to have begun building around 1103.