Official website of Paris-Saclay tourism
Our 10 key attractions
Climb the steps to enjoy one of the destination’s most beautiful views!
Visible from miles around, the Tour de Montlhéry is a striking feature of the Essonne landscape. From mid-April to late October, you can scale the 138 steps to admire a 360-degree view from the top.
The first reference to Château de Montlhéry (Montlhéry Castle) dates from 991. The castle built on a mound in 1015 consisted of a timber tower surrounded by a protective outer wall. It became a royal castle in 1104 and its geographical location between Paris and Orleans quickly made it of strategic interest to the Capetians.
Louis VII and his minister stayed at the castle in 1144. By the 13th century, a masonry keep had been added. Later, Philippe Auguste stayed on more than one occasion, contributing further to the castle’s transformation.
Saint-Louis took refuge at Montlhéry in around 1227, for fear of being abducted in Etampes, and had a chapel built there in 1254.
In 1591, the governor of Paris ordered for the castle to be demolished. Only the keep was left standing and a closer look reveals that it was built over two different periods.
Indeed, the bottom section and the lower two levels were built under Philippe Auguste while the upper part dates from the late 14th century and the construction work which followed the Hundred Years War.
Due to its geographical location and the fact that it reaches an imposing height of 167 metres from the bottom of the mound, the Tour de Montlhéry has been used on many occasions as a scientific testing ground.
1822 = Calculation of the speed of sound by François Agago, Louis-Joseph Gay Lussac and Urbain le Verrier. They fired a cannon from the top of the Tower, at night so that the detonation could be both seen and heard from Villejuif observatory.
1823 = Telegraph tower visible from Fontenay-aux-Roses and Torfou
1874 = From the very top of the tower, Alfred Cornu measured the speed of light from the Paris observatory.
1914 = The inventor, Defieber, tested his parachute model here.