The above examination of the choir, south aisle, and sacristy leads to the belief that they are all of a late period, probably about 1500. The entire building bears evidence of having been in whole or part re-erected about the end of the fifteenth century or the beginning of the sixteenth century, possibly when it became the Cathedral of the Isles in 1506. Some portions, such as the north transept, the north and west sides of the crossing, the wheel stair to the tower and parts of the walling connected therewith, are older; but all the rest, including the east and south arches of the crossing, is of a much later date. Besides the points to which attention has been drawn above, it may be noted that the buttresses of the choir, which from their form may have been raised from ancient bases, have on each angle a single bead on their lower part and a triple bead on the upper part (see Fig. 984). The upper story of the tower, which is admittedly very late, has also a triple bead on the angles of the top story. May it not have happened that the building suffered from some cause, or was intentionally taken down and reconstructed about the end of the fifteenth or beginning of the sixteenth century? Such an event might account for the antique form of the buttresses, which may have been raised from existing portions of old buttresses; while the triple bead on their upper story would show the change of style introduced at the time of the reconstruction. It would also explain the preservation of the old doorway to the sacristy, while the upper parts of the walls were rebuilt. The very irregular appearance of the lower part of the north wall of the choir might also be thus accounted for. The interior string course on the north side, which rises in large steps from the sacristy door, is composed of stones partly enriched and partly plain, as if it formed part of a reconstruction in which old materials had been reused. The clerestory windows, with their ancient forms, are doubtless reproductions of the outlines which formerly existed. The section of the south-east pier of the crossing (see Fig. 998) shows that the south transept is of about the same period as the choir, the round responds in each corresponding with the circular piers of the choir, and the carved caps being very similar in both (see Figs. 989 and 990); and the south wall of the transept, with its late traceried window and buttresses and base course, is evidently of the same period as the presbytery. The mouldings of the mullions are in both cases returned along the sills, an unusual and late arrangement. The rebuilt part of the crossing has arch moulds which correspond in style with those of the south aisle arches, and the sculpture of the caps [Illustration: FIG. 1002.--Iona Cathedral. Chapter House.]