Timeline

Heritage classified

Key figures

Origin and history

The Montlhéry Tower is the last vestige of a castle built from the 10th century on a hill overlooking the Orge Valley, in the present Essonne department. Around 991, Thibaud de Montlhéry, the first lord and forester of the place, erected a castral motte with a tower surrounded by a shirt. This strategic site, controlling the route of Orleans, becomes an issue for Capetian kings. In 1104, Philip I took possession of it, only keeping the tower after having shaved the other fortifications. Louis VI became a permanent member of the royal estate in 1118.

In the 13th century, the fortress was strengthened under Philippe Auguste, with straight courtesines and circular towers. The 30-metre-high dungeon was redesigned in the 14th century by Olivier de Clisson, who added four floors and a round path. The tower served as a refuge in Saint Louis in 1227 and resisted English sieges (1358–1360). During the Wars of Religion, it became a Calvinist headquarters before being partially dismantled in 1591 on the order of Henry IV.

In the 19th century, the tower was classified as a historic monument (1840) and restored by Henri Labrouste, who consolidated its structure and built a terrace. It became a place for scientific experimentation: in 1822 Arago and Gay-Lussac measured the speed of sound, and in 1874 Alfred Cornu studied the speed of light. Closed to the public in 1992, it was renovated between 2000 and 2009 before reopening in 2012, offering a panorama of the region.

Excavations and studies reveal an original pentagonal plane, with an isolated master tower, four circular towers at angles, and a complex defensive system (fossed, drawbridge). The dungeon, divided into six levels, combines hexagonal rooms at the bottom and square at the top, with suspended latrines and mâchicoulis. The materials used – sandstone, millstone, and brick for restoration – bear witness to medieval and modern techniques.

The tower is inseparable from Capetian history and Franco-English conflicts. It is home to prominent figures such as Louis VI, Saint Louis, or Charles the Témeraire, whose battle of 1465 opposed Louis XI. Its decline began in the 16th century, when its stones were used to build the ramparts of Montlhéry. In the 18th century, its ditches were filled to create gardens, before it was safeguarded by the state in the 19th century.

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