The crypt can be the historic inhumation place of the saint on which had been built the monument allowing the welcome of pilgrims. It is the example of the crypt of the abbey Saint-Martial de Limoges which is also a “low-church” where the liturgical ceremonies take place. From this crypt born in a 4th century necropolis we saw a succession of building built on each other.
The crypt might be built for a levelling purpose. Indeed, when the slope of the land is too important, the edification of a crypt enables anupgrade. The builders of the collegial church of Dorat and of the abbey of Solignac used for example this method.
The pilgrims haven’t always had the permission to access the crypt during ordinary days, but they could often see the tomb of the saint from small windows in the choir of the church. Sometimes, as in the abbey of Saint-Martial, the pilgrims requested the guardian of the sepulcher to go in and touch the tomb of the saint.
All the crypts don’t have a direct access via the church.