“The typical form of the broch,” says Dr Anderson, “is that of a hollow circular tower of dry-built masonry, about 60 feet in diameter and about 50 feet high. Its wall, which is about 15 feet thick, is carried up solid for about 8 feet, except where two or three oblong chambers, with rudely-vaulted roofs, are constructed in its thickness. Above the height of about 8 feet, the wall is carried up with a hollow space of about 3 feet wide between its exterior and interior shell. This hollow space at about the height of a man, is crossed horizontally by a roof of slabs, the upper surfaces of which form the floor of the space above. This is repeated at every 5 or 6 feet of its farther height. These spaces thus form horizontal galleries, separated from each other vertically by the slabs of their floors and roofs. The galleries run completely round the tower, except that they are crossed by the stair, so that each gallery opens in front of the steps, and its farther end is closed by the back of the staircase on the same level. “The only opening in the outside of the tower is the main entrance, a narrow, tunnel-like passage 15 feet long, 5 to 6 feet in height, and rarely more than 3 feet in width, leading straight through the wall on the ground level, and often flanked on either side by guard-chambers opening into it. This gives access to the central area or courtyard of the tower, round the inner circumference of which, in different positions, are placed the entrances to the chambers on the ground-floor, and to the staircase leading to the galleries above. In its external aspect, the tower is a truncated cone of solid masonry, unpierced by any opening save the narrow doorway; while the central court presents the aspect of a circular well 30 feet in diameter bounded by a perpendicular wall 50 feet high, and presenting at intervals on the ground floor several low and narrow doorways, giving access to the chambers and stair, and above these ranges of small window-like openings rising perpendicularly over each other to admit light and air to the galleries.” [Illustration: Stone Circle of Stenness] [Illustration: Maeshowe, Section and Ground Plan]