In historic times the oases, according to Sayce, were governed by Egyptian Kings in the eighteenth dynasty (1545-1350 B.C.), and the oldest monuments as yet found in the oases-depressions date from this period. The most important of the earlier remains belong, however, to the Persian epoch, notably the temple of Hibis near the modern village of Kharga, which was built by Darius. Ptolemaic remains are also known in Kharga, but the greater number of the historical monuments date from the time of Roman occupation, when the oases appear to have attained a considerable degree of prosperity, which continued to Coptic times. Since the Mohammedan conquest of Egypt they have fallen into a state of neglect, and with the consequent diminution of the water-supply the population has decreased, and large areas of formerly fertile country have been absorbed by the surrounding desert. It is interesting to speculate on the conditions which obtained in Kharga before the first borings were made, as at the present day we cannot point, so far as I am aware, to a single natural efflux of water on the floor of the depression. Surface-water, of quite a different character from the deep-seated water, is met with at comparatively shallow depths in various localities, and may either represent drainage water from the flowing wells and cultivated tracts, or be water which has escaped from the underground sandstones and found its way to the surface through fissures. Probably it is derived from both sources. In prehistoric times natural springs fed through fissures may have existed here and there within the depressions; and in any case it is probable that prehistoric man obtained sufficient supplies by sinking wells into the upper sandstones, which in some parts of the oasis occur at or near the surface, and contain large quantities of sub-surface or sub-artesian water. Nothing is known as to when flowing wells were first obtained, or by whom the original deep borings were made, and no traces of the implements used have been discovered. Many of these ancient wells, frequently over 120 metres in depth, continue to flow at the present day, although in most cases with a greatly diminished output; a few, however, are still running day and night at the rate of several hundred gallons a minute. In some parts of the oases water-bearing sandstones occur at or near the surface, and from these beds the Romans obtained additional supplies by the excavation of underground collecting tunnels. Subterranean works of this description are found in all the oases, the most remarkable being in Baharia and at Um el Dabâdib and Jebel Lebekha in Kharga. They are frequently of great length, cut throughout in solid rock, and connected with the surface above by numerous vertical air-shafts. Many of the latter measure from 30 to 50 metres in depth, so that the construction of these and the horizontal carrying channels must have involved an immense amount of labour.