Turning now and retracing our steps we pass the staircase by which we descended and make our way round the horse-shoe curve of the apse. On our right we perceive the seven apsidal chapels, of which the first, third, fifth and seventh are the Chapels of S. Mary Magdalene, S. Ives (_see_ pp. 91 _ff._), S. Fulbert (_see_ pp. 69 _ff._), and the Sacristy. They were added in 1194; whilst the second, fourth and sixth are the Chapels of S. Anne, S. John the Baptist, and S. Joseph, and they date from 1020. The window of the Chapel of S. Anne should be noted. S. Anne is represented carrying the Blessed Mary. When we examine the upper church we shall be struck by the importance of the position allotted to S. Anne in glass and statuary--as, for instance, in the great window of the north transept. The explanation is that Louis, Count of Chartres, who died on the fourth Crusade, sent to the Chapter from Constantinople the head of that saint. 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.’