Works of Public Utility — The System probably introduced from Persia — The Bulk of the Works carried out by the Romans — Trenches connecting Wells with Cultivable Lands — Fortress Bores and their Underground Connections — Dêr el Ghennîma — Subterranean Aqueducts of Qasr Gyb — Qasr Lebekha and Um el Dabâdib — Reopening of Tunnel by Sheikh Hassan Hanadi — Sala Abdulla — Nature of Tunnels and Shafts — The Magnitude of the Underground Works — Exploration of the Tunnels — Origin of the Water. Although the Persians and Romans left abundant traces of their occupation of the country in the shape of temples, forts, and monasteries, the determination and energy with which they prosecuted the colonization and general development of the oases is best shown by their attention to works of public utility. At no period in the history of the oases has so much attention been paid to the water-supply. Not content with tapping the deep-seated sources by means of bores, they carried out underground works of considerable magnitude and involving engineering difficulties of no mean order, so as to obtain additional supplies from the sandstones lying at or near the surface. The methods employed were probably introduced from Persia, where underground aqueducts, or ‘kareez,’ for the transference of water from one locality to another, have from an early date been employed. At the same time, judging by the character of the ancient buildings in the immediate neighbourhood of the most important of these works, it seems probable that the latter were for the most part constructed by the Romans. Underground aqueducts are found to some extent in all the chief oases of the Libyan Desert, but in Northern Kharga they far exceed in magnitude anything known elsewhere. In their simplest form they consist of deep trenches connecting the wells with low-lying areas of cultivable land, the object being to tap the bores at the lowest possible levels, in order to obtain the greatest discharges. Thus, although a bore, originally sunk on comparatively high ground for the purpose of irrigating a particular area of land, might through one cause or another have ceased to flow, it could still be made available for any low-lying area farther afield by the simple expedient of tapping it below the surface by means of a trench or tunnel. This practice was frequently resorted to.