It is to be observed that the type of Round Tower peculiar to Scotland, and known by the name Broch, differs totally, and in all its essential features, from the tall, slender, round Towers of Ecclesiastical construction in Scotland and Ireland. The Brochs are dry-built, the Ecclesiastical Round Towers are lime-built. No hewn stone is used in the construction of a Broch; the doors and windows of the Ecclesiastical Round Towers are often of hewn stone, and sometimes ornamented with sculptures. The Brochs have their chambers, stairs, and galleries in the thickness of the wall enclosing the central area; the lime-built Round Towers possess none of these features. The Brochs have their doorways always on the ground and their windows opening to the interior area; the Ecclesiastical Round Towers have their windows opening in the exterior wall, and their doors placed at a considerable height above the ground. There is thus no point of similarity between the two types of structure except their external roundness.
In Scotland the area which is chiefly occupied by the Brochs was peculiarly exposed to similar occurrences. Over the whole of the northern and western districts there ebbed and flowed continuously for centuries a species of irregular intermittent warfare, consisting chiefly of plundering forays by bands of foreign marauders. And as the special association of the Round Towers of Ireland with the ecclesiastical sites of the country supplies the clue to their special purpose, the Brochs of Scotland have also their special association from which their special purpose may also be fairly deduced. Although they are often placed in situations of natural strength, yet, as a rule, they mark the area of the best land in the districts in which they are situated. This is specially true of their local distribution in Caithness, while in Sutherland we see them thickly planted in the fertile straths, and following the courses of the rivers to distances of twenty-five or thirty miles inland. They are therefore the defensive strongholds of a population located upon the arable lands, and not in the mountain fastnesses of the country; and their peculiar nature as exceptionally secure places of refuge for non-combatants and cattle, and for storage of produce, explains the fitness of their association with the arable soil of the area in which they are most abundantly present. Against such oft-recurring but transient dangers to the cultivators and to the produce of their soil there could be no more effective system of defence provided than a multitude of _safes_, which should be burglar-proof, and big enough to contain the families, goods, and cattle of their proprietors.[77]