Ruins of columbaria are of frequent occurrence in many parts of Kharga, and judging from the size and shape of the bricks used, belong to the same period as the forts and monasteries. They are generally of considerable size, the inner walls being built so as to provide tiers of cubical niches to serve as nesting-places for the pigeons. Examples may be seen at Ain el Burg and Ain Tabashîr in the Meheriq district; in the Bellaida country, and near Ain Khenâfish; on the slopes of the Gorn el Gennâh; and near the village of Dush at the south end of the oasis. These ancient pigeon-houses are called ‘Burg’ by the natives, the Arabic name for dovecot being ‘Burg Hamâm.’ That the oases were very flourishing under the Roman Empire is shown by Olympiodorus, who lived in the reign of Theodosius II. (A.D. 408-450), and was born in Upper Egypt. Writing of the Great Oasis, he calls attention to its salubriousness, to the abundance of sand everywhere, and to the numerous wells, which, sunk to a depth of 200, 300, or even 500 cubits,[7] pour forth streams of fresh water at the surface, which is used in rotation by the owners for the irrigation of their fields. Barley, he avers, is sometimes sown twice a year, and millet almost always three times. Writing of the irrigation, Olympiodorus remarks that in this region the sky is always cloudless, and that the great fertility of the land is attributable to the fact that the peasants water their little enclosures every third day in summer, and every sixth in winter. The same writer states that dials were made in the oasis. The presence of marine shells in the rocks of the surrounding deserts led Olympiodorus to conjecture that the oasis was formerly an island, separated by the sea from the rest of Egypt, and he recalls the fact that the place was called by Herodotus ‘the Island of the Blessed.’ Strabo writes of the Libyan Desert thus: “This continent resembles a panther’s skin, as being spotted with inhabited districts, insulated in the midst of a sandy soil and arid deserts; the Egyptians call these cantons ‘Auasis.’” He refers to the Great Oasis as follows: “In a parallel line with Abydus, and distant about three days’ journey across the desert, we find the first of the three Oases of Lybia; it is a spot well inhabited, well supplied with water, and producing wines and other commodities in sufficient abundance.” With the withdrawal of the Roman garrisons and the Mohammedan conquest decay set in, and, as Sayce remarks, the aqueducts became choked, the fields were neglected, and malarial fever invaded a district which had at one time been regarded as a health resort.