The regularity of the building of this burgh, and the architectural knowledge it implies, prevent our ascribing it either to the Stone or even to the Bronze age; but we find in Scotland itself more ancient examples, if we may so express ourselves, of domestic architecture. These examples are subterranean dwellings, made of rough-hewn stones of considerable size, laid down in regular courses, to which the names of _earth-houses, Picts’ houses_, and _weems_ have been given. The walls converge towards the centre, leaving an opening at the top, which was covered in with large flat stones. These dwellings are certainly of earlier date than the burghs, and the discovery of a _Picts’ house_ actually beneath the ruins of a burgh enables us to speak with certainty on this point. In Ireland similar proofs have been found of the great antiquity of roan. More than one hundred towers have been found in that country, all built of large stones, and varying in height from seventy to one hundred and thirty feet, with a diameter of from eight to fifteen feet. The most diverse origins have been attributed to these towers, from prehistoric times to the centuries immediately preceding the Christian era; from the time of the Druids to that of the Friars. According to the point of view of different archæologists, they have been called temples of the sun, hermitages, phallic monuments, or signal towers. We meet with a similar problem in considering the _nurhags_, as in considering the burghs. They have been justly called a page of history, written all over the surface of Sardinia by an unknown people. Count Albert de la Marmora counted three thousand of them a few years ago, and more recent explorers tell us that this number is greatly exceeded. Like the burghs, which they strangely resemble, the _nurhags_ are conical towers with very thick walls made of huge stones, some Hewn, others in their natural state, arranged in regular courses without mortar. On entering one of them we find ourselves in a vaulted room, which looks exactly like one half of an egg in shape. In the upper stories are two, and sometimes three rooms, one above the other, to which access is gained by steps cut in the walls. The whole structure is crowned by a terrace (Fig. 53). We must add that the entrance to the _nurhag_ is through an opening on a level with the ground, and so low that one can only go in by crawling on the stomach.