Pierre aux Moines, Neolithic menhir in Clamart, France

Pierre aux Moines is a 2.20 m tall Fontainebleau sandstone block in the Bois de Clamart, within the Meudon Forest on Clamart territory. It measures 2.10 m wide at the base and 0.70 m at the top, with a thickness of 0.55 m at the base and 0.28 m at the top, and is buried 0.25 m deep. Its slightly flattened top likely results from centuries of use as a knife sharpener. Nearby lie other fallen blocks, including a 1.85 m by 1.60 m sandstone slab.

Two standing stones, the Pierre aux Moines and the Pierre de Chalais, are documented in the Meudon forest; the 1708 map by Nicolas de Fer places the Pierre aux Moines at a crossroads that disappeared with the building of avenue Claude-Trébignaud around 1960. By 1865 Eugène Robert no longer mentioned the Pierre de Chalais, and the visible block is now considered to be that stone, the original Pierre aux Moines having vanished. Classified as a monument historique in 1895 under the name Pierre aux Moines, it fixed the confusion.

The name Pierre aux Moines (Monks' Stone) was attached to this block, though it is now identified as the Pierre de Chalais. On its north-northeast face a U-shaped groove, 26 cm high and 21 cm wide, has been read as a funerary collar; the Abbé Breuil claimed to see ocelli on the upper part, but none are visible today.

The stone stands in the Bois de Clamart, the Clamart section of the Meudon forest, on the Clamart commune in Hauts-de-Seine. The old crossroads where early maps placed it vanished when avenue Claude-Trébignaud was built around 1960, so approach from the woodland paths of the Bois de Clamart rather than from the avenue. The site became easier to reach after the clearing of 1893.

The stone visible today is probably not the original Pierre aux Moines: it is the Pierre de Chalais, and the true Pierre aux Moines vanished. The 1708 map by Nicolas de Fer placed it at a crossroads erased around 1960 by the avenue Claude-Trébignaud. The 1895 listing kept the wrong name.