Covenant of Montverte - location in RL

I'm on a holiday in Normandy, and will drive from Caen to Alençon and pass the area where the covenant of Montverte is supposed to be located (Lion and the Lily p. 58.) Does anyone know if this covenant is based on a real historic site and how to find it? If so, it would be cool to visit it.

It's not based on a real historical site, sorry!