At the beginning of this period, the bell-towers were of very little importance; but gradually we find them rising higher and higher, and attaining to great elevations. Some cathedrals on the borders of the Rhine, and the Church of St. Etienne at Caen, are examples of the extraordinary height to which these towers were built. In principle, we may add, there was only one bell-tower (Fig. 301); but it generally happened that two were given to churches built or restored after the year 1000: St. Germain-des-Prés had three bell-towers--one over the portal, and one at each side of the transept; certain churches had four and even five bell-towers. Norman bell-towers are generally square, exhibiting, in stories, two or three ranges of round-arched arcades, and terminating in a pyramidal roof resting on an octagonal base. The Abbey of St. Germain d’Auxerre possesses one of the most remarkable bell-towers of the Norman style; then come, although built subsequently to the principal edifice, those of the Abbaye aux Hommes, at Caen. [Illustration: Fig. 301.--Ancient Church of St. Paul-des-Champs, at Paris, founded, in the Seventh Century, by St. Eloi. Restored and in part rebuilt in the Thirteenth Century.] The sun’s rays penetrated into the Norman church first through the _oculus_,[50] a vast round opening intended to admit light into the nave, and situated above the façade, which generally rose in the form of a gable above one or several rows of small columns on the exterior. A series of lateral windows opened on the side-aisles of the edifice; another was pierced on a level with the galleries; and a third between the vaulted arches of the nave. The crypt, a sort of subterranean sanctuary, which generally contained the tomb of some beatified saint, or of some martyr to whom the edifice was dedicated, formed very often an integral part of the Norman church. The architecture of the crypt, which had for its ideal object to recall to the mind the period when the offices of the Christian religion were performed in caverns and in catacombs, was generally of a massive and imposing severity, well suited to express the sentiment which must have presided over the earliest Christian buildings.