features that are closely similar. But as we are dealing with buildings that are in ruins, and, as it appears, with a class of buildings of which no complete example is now known to exist, it is important to determine if possible whether there may be sufficient ground for assigning to the class the general feature of height, of which, in the majority of cases, no direct evidence now remains. [Illustration: Fig. 169.—Broch known as Cole’s Castle, Sutherlandshire. (From a Sketch by Dr. Arthur Mitchell.)] [Illustration: Fig. 170.—Dun Dornadilla, in Strathmore, Sutherlandshire. (From a Sketch by Dr. Arthur Mitchell.)] There is distinct evidence on record that a number of these massively built towers were of considerable height. George Low, in 1774, says of the ruined tower or Broch of Burraness, in the island of Yell, in Shetland, that it had an inside diameter of 31 feet, a thickness of wall of 10 feet, and a total height of 20 feet. Of the Cullswick Broch he says that its internal diameter was 26 feet 6 inches, its thickness of wall 18 feet, and the total height remaining 23 feet. Castle Cole (Fig. 169), at the junction of the Blackwater and the Brora, was then 15 feet in height, and part of it still remains of about that height. Dun Dornadilla, in Sutherlandshire (Fig. 170), as described by Mr. Cordiner in 1776, and Mr. Pope of Reay, in 1777, had an internal diameter of 27 feet, and the total height then remaining was estimated at 25 to 30 feet, with three galleries and part of the stair. Maitland, in 1757, describes Dun Alisaig, in Ross, as being 30 feet internal diameter, with 12 feet thickness of wall, and three of the galleries remaining, which implies a height of 25 to 30 feet. Dun Carloway, in Lewis, was 40 feet high in the end of last century, and showed the plan of its galleries with their vertical ranges of windows almost as completely as Mousa. Judging from these examples, which still have, or which in recent times have had a considerable portion of their height remaining, and taking into account the quantity of material which envelops the bases of most of those that have been reduced to the condition of mere mounds of ruin, it seems established by evidence that there were many cases in which the total original height could scarcely have been less than that of Mousa, and that height, as well as bulk, was one of the main features of the typical structure. These examples will suffice to convey a clear idea of the distinctive features of the type of structure with which we are dealing. Its main features of distinction, by which it separates itself from all known types, are (1) that it is a circular tower of dry-built masonry, wide and lofty, and enclosing within it a central area open to the sky; (2) that all its apertures, except the external opening of the entrance to the central area, look into this enclosed interior court; and (3) that its chambers, stair, and galleries are contained within the thickness of this enclosing wall.