A staircase in the south-west tower leads up into the roof of the aisles, which now partly blocks up the too large clerestory; and passing through this, and then over the roofs of the sacristies, we reach the exterior of the chevet and the fortified eastern wall. Over the sacristies is some original stone roofing, of an extremely good, and, so far as I know, almost unique kind, with which it, seems very probable that the whole of the roofs were originally covered. But it is now, as well as all the others, protected by an additional timber roof covered with tiles, and is not visible from the exterior. This roofing is all laid to a very flat pitch with stones, which are alternately hollowed on the surface for gutters, and placed about eight and a half inches apart, and other square stones, which rest on the edges of the first, so as to cover their joints. The stones are of course all of the same length--two feet seven inches--and set over each other so as to form a drip. The cornice at the eaves of this roof is very well managed, and looks as if it were of the thirteenth century. Its construction reminded me much of the stone guttering so frequently seen in the early Irish buildings, and which, being so much less perishable than lead, has often preserved them, where the common English construction would long ere this have involved the whole building in ruin. [Illustration: CATHEDRAL OF SAN SALVADOR AVILA--Ground Plan of Church and Cloister &c. Plate 3 Published by John Murray. Albermarle St. 1865.] The cloister on the south side of the nave is much decayed and mutilated. It was built probably in the early part of the fourteenth century, and has good traceried windows, generally of four lights, but blocked up, and with all their cusping destroyed. On its east side is a fine fifteenth century chapel, with an altar at the south end, and a passage through its other end, screened off by an iron Reja, leading to the priests’ rooms, and so round to the sacristies. The windows of this chapel are covered with a rude ball ornament, constantly seen in works of the fifteenth century.