Many conjectures have been made as to the use of these towers. Were they temples in which to worship, or trophies of victory? Their number is against either of these hypotheses. Were they then habitations or towers of observation? Not the former certainly, for no one could live between walls sixteen or twenty-two feet thick, shut out from air and light. Some travellers think they were tombs, but excavations have brought to light no bones or sepulchral relics. We can compare them to nothing but the Towers of Silence, on which the Parsees expose their dead to the birds of heaven, which are ever ready rapidly to acquit themselves of their melancholy functions. [Illustration: 53.] Nurhag at Santa Barbara (Sardinia). The origin of the _nurhags_ is as uncertain as their use. Diodorus Siculus considered them very ancient, and one fact has come to light in our day which enables us to arrive at a somewhat more exact decision. The island of Sardinia was taken by the Romans from the Carthaginians in 238 B.C., and an aqueduct, the ruins of which can still be seen, was built by the conquerors on the foundations of an ancient _nurhag_, so that the latter must belong to an earlier (late than the third century before our era. Fergusson, who speaks with authority on everything relating to the monuments of the Stone age, assigns the _nurhags_ to the mystic times of the Trojan War. In all probability they were built by an invading people. La Marmora thinks these invaders were the Libyans; M. de Rougemont, in his history of the Bronze age, says that the curved vault is the characteristic feature of Pelasgian architecture, which is often confounded with that of the Phœnicians. Although any final conclusion would be premature, we ourselves think that the builders of the _nurhags_ belonged to the great stream of emigration from the East, the course of which is marked by megalithic monuments in so many parts of the world. In some instances, _nurhags_ were surrounded by cromlechs, of which most of the stones have now been thrown down. Some of these stones bore prominences resembling the breasts of a woman. The accumulations of earth and rubbish about the _nurhags_ are, some of them, from six to ten feet high. In the lower deposits have been found coarse pottery, with no attempt at ornamentation, fragments of flint, and obsidian hatchets of black basalt, or porphyry of the Palæolithic type, arrow-head, flint knives, stones used in slings, and numerous shells; whilst in the upper deposits were picked up black pottery and fragments of bronze belonging to the transition period between the Stone and Metal ages.