Opposite the Sacristy is the entrance to the _Martyrium_ or Chapel of S. Lubin (_see_ p. 36), which is immediately under the sanctuary. Of this chapel enough has been or will be said.[13] At this point it will suffice to call attention to the architectural features which serve to illustrate its history. First, the fact that you descend into it by a modern entrance, which has replaced the old staircase and doorway; and secondly, the depth of the base of the round column on the right, indicating the original level of the primitive church floor; thirdly, the hiding place for the treasure; next, the fourth-century wall, with its layers of thin horizontal Roman bricks; and lastly, the circular wall and the ninth and tenth-century piers. The Gallo-Roman wall on the west is probably a portion of the old _enceinte_ of the town.
Going westwards on leaving the martyrium, we pass a staircase on our right and the Puits des Saints Forts on the left, behind the wall of the altar of Notre-Dame-de-Sous-Terre. When this wall was built and the well concealed in the seventeenth century, the circular passage by which the chapel could be approached had also to be made, and the masonry was so treated as to suggest the natural rocks of the old Druidical ‘grotto.’
The chapel is at the end of the northern gallery (eleventh and twelfth century), which runs from the base of the _Clocher Neuf_. It is lit by two long rows of pendant lamps. Here, then, is that mysterious shrine which Boutrais has so well described. Here is that famous statue which for a thousand years has drawn countless myriads of pilgrims from all parts of the earth.[14] Kings and commons, rich and poor, scholars and Crusaders, sinners and saints unnumbered have knelt at this shrine since the day when Fulbert, having completed his crypt, left, it is said, the ‘Statue of the Druids’ in the same place as that in which the Gallic priests had held their assemblies _in finibus Carnutum_, on Carnutan territory. That statue was held in honour till the year 1793, when it was burnt by the Revolutionists before the _Porche Royal_. The present Madonna was made on the model of the old, and erected in 1857, after the crypt, which for sixty years had been used as a cooper’s warehouse, was restored to its sacred uses. On the north wall may be seen the traces of three twelfth-century windows, which were blocked when the north porch was built; on the south wall traces of twelfth-century frescoes. Other frescoes in the chapel are recent symbolic work by M. Paul Durand. The vaulting was painted in the seventeenth century.