Digging into the earth, studying a stone, recording a trace, returning a fragment to its context: archaeology often advances in small clues. The Journées de l’archéologie invite you to explore the discipline up close, through guided visits, discussions, workshops and site openings. In 2026, they will be held on the weekend of June 12–14, 2026, offering a chance to uncover the secrets of a mysterious monument.
Visible from afar, the Montlhéry Tower is one of the premier heritage landmarks of southern Île-de-France. The castle sits atop a height overlooking the Orge Valley, in the old Hurepoix region. Its history stretches back to the Middle Ages, beginning with an early fortification and later a reconstruction attributed to the era of Philip II Augustus in the early 13th century.
The site bears the telltale signs of a defensive design: ramparts, towers, a courtyard, guarded access, and a commanding position. Over the centuries, the castle endured sieges, was repeatedly altered, and later fell into serious ruin. The Hundred Years’ War, conflicts in the 15th century, and the stones being quarried for other uses under François I all fed its deterioration.
Listed as a historic monument in 1840, the castle is now owned by the state. It also carries a remarkable scientific legacy: in the 19th century, the site hosted experiments on the speed of light and of sound.
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This medieval tower, offering a breathtaking panoramic view of Essonne, was once used to measure the speed of light.
Perched atop a 30-meter-high hill, the Montlhéry Tower offers a breathtaking panoramic view of Essonne and the Île-de-France region. This historic medieval relic, officially listed as a Monument Historique, once served as a laboratory for some of the greatest scientists of the 19th century. Whether you're interested in its history, planning a visit, or just taking a leisurely walk, here's everything you need to know. [Read more]
Book your spot for a one-of-a-kind guided tour. An archaeologist will guide you through the excavation sites at Montlhéry Castle. You’ll also have the opportunity to view a curated selection of archaeological artifacts from the latest dig carried out in 2019.
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Dates and Opening Time
On June 13, 2026
Location
The Montlhéry Tower
10 Allée de la Tour
91310 Montlhery
Official website
www.montlhery.fr
This medieval tower, offering a breathtaking panoramic view of Essonne, was once used to measure the speed of light.
