Because of excellent proportions, the church appears larger than in reality. The exterior is Romanesque. Two time-stained towers of the XI century mark the angles between transept and choir, an arrangement derived from Rhenish churches. At the west façade is a beautiful XII-century tower. It was building while the nuns were proceeding to tear down a decrepit apse in order to erect the present east end of the church. In that new apse appeared the much-discussed early ribs. A record tells that relics were installed in the church in 1122, and it was probably then that the new works were finished. Ambulatories had come into favor during the first third of the XII century, when need was felt for a suitable corridor for pilgrims to encircle the altar whereon relics were exposed. Now to vault a curving aisle was no easy task, owing to the trapeze shape of each section. Morienval's ambulatory must have been designed to hold extra altars, since entrance to the aisle is blocked at both ends by the towers, and the passage is so narrow that only one at a time can walk in it. There are no apse chapels. The sculpture is archaic. Some of the capitals show interlacings, and some are of the pleated type popular in Normandy. The diminutive corridor has four small bays whose clumsy intersecting vault ribs are of the size of the average stovepipe. They curve strangely, and two of the keystones are not in the axis of the passageway, nor has elasticity yet been wholly achieved, since the ends of the ribs plunge into the web of the vault. Over the choir, consisting of one large bay, are intersecting ribs that appear to be posterior to those of the ambulatory. They, too, are rude and large, but are wholly detached from the cells. M. Lefèvre-Pontalis thinks that the ambulatory diagonals are contemporary, and owe their more archaic character to the difficulty of vaulting a curved passage. So swiftly did the early architects acquire skill in the new system of building, that when a chapel was erected on the northern arm of Morienval's transept, at the end of the XII century, each diagonal had become a single slender torus, virile and graceful.