The church of the monastery was finished in 1040, and is very archaic. It underwent, however, additions in 1157, when the curious vaulting was added. As a doubt was entertained whether the piers would sustain it, they were strengthened, and smaller arches added beneath those first erected. The church reminds one of the monolithic church of S. Emillon on the Garonne. The same square, massive piers rising to a great height, quite unadorned, support the round-headed unmoulded arches. Above each arch is a small, round-headed clerestory window. The church consists of five bays, and the nave has side aisles, out of which open chapels of much later construction. There was in the church at one time a richly carved altar-piece of the fifteenth century. But when the present detestable roccoco retable was erected, this was destroyed. Some of the panels were happily preserved and affixed to the pillars in the nave. Outside the church the western portal is early, with a triangular lintel, on which is cut a shield with A.ω between A and A. The meaning of these double A’s is not understood. In the diminutive yard without, behind is a grating, of an early sarcophagus that contained the bodies of saints Abdo and Senen. It possesses the curious property of filling with water, which can be drawn off by a tap at the side to supply bottles brought by pilgrims, who consider the water as efficacious in many maladies. How it is that the sarcophagus thus fills with water is not known; probably the clergy of the church do not themselves know, as the heavy lid has not been removed for centuries, nor the stone coffin shifted from the spot where it now stands. But the greatest beauty of the church consists in the large cloister on the north side, of the thirteenth century. The arches are pointed, and rest on graceful pillars with dainty foliaged capitals, all of marble, and coupled. The cloister is not vaulted. This cloister was begun in 1261, but was not completed till the beginning of the fourteenth century. The patrons of the church are SS. Abdo and Senen, Persian saints who suffered under Decius in 252. In the reign of Constantine the Great their relics were enshrined in Rome, and the marble sarcophagus that contained them still exists there, and their remains are in the church of S. Mark, Rome; but also here. Their day, 30 July, is a high festival at Arles, when the sleepy town is full of animation, and dances take place in the public square; then can be seen the red _barretina_ and the gaily-coloured kerchiefs of the women.