Now, we come to the great puzzle, the remains of the octagon building, which was commonly called the Baptistery. Sir William Wilde, who saw it as it was in 1848, calls it the oldest and by far the most interesting architectural remains in the whole place; and he goes on to describe it:[5] "This octagonal structure, of which only four sides remain, consists of a colonnade or series of circular-headed arches, of the Roman or Saxon character, enclosing a space of 29 feet in the clear, and supporting a wall which must have been, when perfect, about 30 feet high. Each external face measures 12 feet in length, and was plastered or covered with composition to the height of 10 feet, where a projecting band separates it from the less elaborate masonry above. The arches[6] are carved in sandstone, and spring from foliage-ornamented capitals, to the short supporting pillars, the shaft of each of which measures 3 feet 5 inches. The chord of each arch above the capitals is 4 feet 3 inches. Some slight difference is observable in the shape and arrangement of the foliage of the capitals, and upon one of the remaining half arches were beautifully carved two birds; but some Goth has lately succeeded in hammering away as much of the relieved part of each, as it was possible. The arches were evidently open, and some slight variety exists in their mouldings. Internally a stone finger-course encircled the wall, at about six inches higher than that on the outside. In the angles between the arches there are remains of fluted pilasters at the height of the string-course, from which spring groins of apparently the same curve as the external arches, and which, meeting in the centre, must have formed more or less of a pendant, which, no doubt, heightened the beauty and architectural effect. Like the pillars and stone carvings in the Chapter-house, this building was also painted red and blue, and the track of the paint is still visible in several places. The upper story, which was lighted by a window on each side of the octagon, bears no architectural embellishment which is now visible." He then adds, how Archdall, in his _Monasticon_, asserted that a cistern was placed on the upper story, whence water was conveyed by pipes to the different parts of the monastery; but shows how such an arrangement would have been impossible, on account of the weakness of the walls, and the position of the windows.