_Archæologia Scotica_, vol. v. pp. 178-197.
Whatever may be the effect of future discoveries in increasing the number of examples in the district south of the Caledonian valley, it is clear that the principal area of the type lies within the region to the north of that valley, comprehending the five northern counties of Scotland, and including the northern and western Isles. Within that area they are known to exist abundantly, beyond it sparsely. Out of Scotland the type is totally unknown. It is a type possessing features so distinct and peculiar, so numerous and well marked, so pronounced in their absolute individuality, that if it exists anywhere it is capable of being instantly recognised. But no single instance occurs in Ireland, or Wales, or Cornwall. No trace of it is found in England, France, or Scandinavia. It is absolutely confined to Scotland alone.[73] Having thus established the essential features of the typical form of the Broch structure and determined the area to which it is exclusively confined, I now proceed to notice a few other examples possessing features which may not have been present or prominent in those previously described.
The Nuraghi of Sardinia are round towers built of uncemented stones. They are exceedingly numerous in the island, and it has been occasionally asserted that they bear a remarkable resemblance to the Scottish Brochs. It is true that they are like the Brochs externally, because they are round towers, (see Fig. 176), but they possess none of the characteristic features of the typical Broch structure. They contain vaulted and windowless chambers placed vertically above each other in the centre of the tower. The access to these chambers is by a winding stair, which traverses the thickness of the wall completely round the central chambers. Sometimes they have a more complex structure, consisting of a central tower rising from a square basement, with chambers also in the basement, as shown in the accompanying section (Fig. 179). It is thus apparent that the typical Nuraghe differs completely in idea from the typical Broch. Although the external form may be in some cases similar, the essential features of the Broch are not found in any one instance in the Sardinian Nuraghi. No Broch has vaulted chambers disposed vertically over each other in the centre of the tower, and no Nuraghe has its centre open, and its chambers, stairs, and galleries arranged in the ring of walling surrounding the central court and windows looking into it as the Brochs have.