The crypt was likely part of the original church, constructed shortly after the foundation around 1022.The body of the crypt is presented here as it exists today. The stairs have been reconstructed to run parallel to the crypt rather than perpendicular as they are now. This is more consistent with contemporary arrangements. The current condition probably arose from the placement of the choir piers, which would have interfered with the original stairs. There is nothing in the crypt to suggest that it cannot date to the time of Robert the Pious, in particular the traditional date of the foundation of the church in 1022. The painting is clearly later, but the crypt itself is consistent with others of the period, and the carving of the capitals has a primitive character that is also consistent with the period. The niche at the east end of the crypt was probably originally a window. As such, it must have been above ground at that time. The site currently slopes from west to east but the original grade was probably lower, allowing for the window to be exposed.

At some point while the choir was being constructed the stairs to the crypt were modified.