_Doorways._--In form these are similar to the doorways we have described as characteristic of the early churches, but they are generally more highly ornamented, and appear to have been furnished with double doors. They are placed almost invariably at a considerable elevation above the ground. A flat projecting band, with a small bead-moulding at the angles, is the most usual decoration; but in some instances a human head, sculptured in bold relief, is found upon each side of the arch. A stone immediately above the doorway of Antrim tower exhibits a cross sculptured in _alto-relievo_; and at Donaghmore, in Co. Meath, a figure of the Crucifixion, in bold relief, occupies a similar position. This style of decoration may have been much more common than is generally supposed, as, of the number of towers remaining in Ireland, the doorways of at least one-third have been destroyed. Concentric arches, with chevron and other mouldings, occur at Timahoe and at Kildare. * * * * * [Illustration: Window, Round Tower, Cashel.] _Windows and Apertures._--Generally speaking, these are similar in form to the windows in contemporary churches--with this difference, that they never splay, and that the arch-head in numerous examples differs in interior form from that of the exterior. The windows in the earliest towers are square-headed or triangular, and in the latest they are well formed, and of cut stone. The tower was divided into storeys, about 12 feet in height, the floors of which were supported by projections of the masonry or by brackets. Each storey, except the highest, was generally lighted by one small window; the highest has generally four of large size. A conical roof of stone completed the building. The tower usually rested on a low circular plinth; the walls varied in thickness, from 3 to 5 feet; the lowest storey had no aperture, and sometimes its space was filled by solid masonry. The earliest towers were built of rubble masonry; and the spaces between the stones were filled with spawls; little mortar was used in laying the courses, but grouting abundantly. In the latest towers fine ashlar masonry was used, like the Norman work of the twelfth century; a few have external string courses, as in the perfect tower at Ardmore, County Waterford. About seventy round towers still remain, thirteen of which are perfect, of which ten retain the original conical cap. * * * * * [Illustration: Clondalkin Round Tower.]