The upper story has a range of windows, giving light to the nave, and is called the clere-story. Thus a spectator standing in the nave and looking toward either side, will see before him the main arcade and side windows, above the arcade the triforium, and above this the clere-story, beautifully illuminated and crowned with the nave, vault or roof. The great size and height give sublimity to the sight. The east arm of a cathedral is that to which most importance is attached, and has greater richness and more elaborate finish. When the termination is semi-circular or polygonal it is called an apse or apsidal east end. Attached to some of the side walls it is usual to have a series of chapels, partially shut off from the main building, yet of easy access. Tombs and enclosures connected with them, called chantry chapels, are met in various positions, especially in the eastern arm. Below the raised floor of the choir there is a subterranean vaulted structure called the crypt. Passing to the exterior, the principal doorway is in the west front, deeply recessed, and elaborate in design. There are also doors in both ends of the transept, and one or more side entrances. In a complete cathedral the grand architectural effect is principally due to the towers with which it is adorned, the most massive standing at the crossing of the transept. To cathedrals and abbey-churches a group of monastic buildings was attached; sometimes very expensive and in the best style of the art. The most important of these is the Chapter House, which is frequently lofty and highly ornamented. The extent and arrangement of the monastic buildings adjoining the cloister vary with the needs of the different order of monks. The monk’s dormitory was on the east side of the great cloister, the refectory and kitchen on the south, and on the west the great cellar, and a hospitum for the entertainment of guests. The house for the abbot, the infirmary, the school building for novices, with its chapel, and more remotely the granaries, mills, bake-houses, offices, garden, cemetery—taken all together, a monastery shows an extensive group of buildings well arranged for the purposes intended. Some military and domestic buildings are also of great interest. In those centuries dwellings of much consequence were all more or less fortified. Some were built with a lofty square tower, called a “keep,” and capable of standing an assault or a siege. The number and character of the buildings in the enclosure around the keep of course depended on the ability of the proprietor. The outer buildings of the Tower of London, though much modernized, give a good idea of what a first-class castle grew, by successive additions, to be. In those erected near the close of the thirteenth century, the square tower was abandoned, and better provision made for the comfort and convenience of the occupants.