The eastern and northern façades of the Merveille are models of severe and virile beauty; a massive grandeur characterises them, especially striking and impressive in the northern front as viewed from the sea. The vast walls of granite (the material used throughout, save in the inner walk of the cloister) are pierced with windows varying in shape according to the character of the rooms they light. Those of the dormitory are very remarkable. They are long and narrow, and affect the aspect of loopholes, deeply splayed outwards; the peculiar form of the honeycombed window-heads suggests a reminiscence of Arab types seen by the French Crusaders in Palestine. The thrusts of the interior vaulting are met on the exterior by massive buttresses, the vigorous profiles of which contribute greatly to the nobility of the general effect.
These formidable façades were practically fortifications, but the Merveille was further defended to the north by an embattled wall, flanked by a tower which served as a post for watchmen, to which the covered ways running round the base of the western buildings converged.
In the middle, on a level with the north-west angle of the Merveille, a châtelet, or miniature keep, now destroyed, guarded the rugged passage between embattled walls which led to the Fountain of St. Aubert, and was known as the Passage du Degré (passage of the stairway).
The various buildings of the abbey which were added in the fourteenth century, after the construction of the Merveille, are: the abbot's lodging, with its offices on the south, and certain military works which completed the defensive system. In the fourteenth and fifteenth centuries these were gradually extended to the walls of the town, as we shall see in Part III., "Military Architecture."