We have already seen that many of these towers were built in positions that were naturally strong. One of the most remarkable of these is the Broch of Cole’s Castle in Strathbrora, Sutherlandshire (Fig. 178), which has been already referred to. It is situated on the top of an isolated eminence, precipitous on one side, and defended on the side which is less precipitous by a double fortification of dry-stone walling. Others whose situations made them capable of being so defended were protected by ditches and embankments. The Broch of Snaburgh, in the island of Unst, in Shetland, which stands on a promontory projecting into the loch, is protected on the land side by a wet ditch and a rampart of large stones. The Broch of Burraness, in the same island, is strengthened on the land side by two deep ditches and high embankments. The Broch of Cullswick was protected by a ditch 13 feet wide, and a rampart of earth and stones completely encircling the base of the tower. The Broch of Burraland, which stood on a promontory in the loch, had a double rampart and a double wet ditch on the land side, both well defined. The Broch of Yarhouse, in Caithness, stood on a low flat promontory projecting into the loch, and was cut off from the land by a deep ditch from 25 to 30 feet wide, and had its doorway further protected by a long covered way. The Broch of Clickamin, at Lerwick (Fig. 179), although situated on an island in the loch, was fortified by a wall completely surrounding the island. Within this outer wall of defence there is an outwork or guard-house, in form a segment of a circle, 43 feet on its convex face, connected with the outer wall by a passage. The outwork is 19 feet wide at the passage through it, slightly narrower at the ends. The passage is 8 feet high, and about 5 feet in from the outer face of the work it narrows to 2 feet 11 inches, with checks for a door. Behind these are holes in the opposite walls for a bar and a slit in the roof of the passage. Besides these two exterior defences the doorway of the tower itself had checks and a sill for a door about 10 feet within the outer opening of the entrance passage through the wall of the Broch. This passage is 4 feet 10 inches high, and the opening between the door-checks is 2 feet 11 inches wide at the bottom and 2 feet 6 inches at the top, with bar-holes on either side. [Illustration: Fig. 179.—General plan of Broch of Clickamin, near Lerwick, Shetland, showing the walled island and causeway leading to it. (From a plan by Sir H. Dryden.)] [Illustration: Fig. 180.—Diagrammatic Section of East Broch of Burray. (From _Archæologia Scotica_, vol. v.)]