A vast Romanesque church begun in the XIth century by the lords of Montlhéry on the site of a Druidic place of worship, to house a precious relic, a piece of the veil of the Virgin Mary, the beginnings of the very rich reliquary (the second largest in France).
Sculpted XIIIth century tympanum featuring the dormition and the glorification of Our Lady.
As a staging point on the pilgrim route for Santiago de Compostella the church is famous for its pilgrimages.