The common Châtillon derives its etymology of latin castellum which reminds us that from the Xè stood here a century fortress. A cartulary of 1192 reported its existence under the name Castellionem. The term of Montrouge, Mons Rubeus Romans, seems to be due to the color of mud that left the Seine on the slopes of the plateau. Terrain career, it remained bare for a long time and few lived. A text of 1194 already reported the presence of a priory of Saint-Lazare in Monte Rubeo. A small hamlet was formed around the current parish church and became the XllIè century. A parcel of the town was annexed by Paris in 1860.