To the Roman period may possibly belong a large crude-brick rectangular enclosure close to Ain el Haiss. This building is 75 paces square, with a main door on the west side, and has walls about 2 metres in height. The brickwork is peculiar, a course of stretchers three bricks deep being followed by two courses of headers set on edge, with one or two rows of bricks in a perpendicular position down the centre; the walls are 50 centimetres thick. The interior of the place is a large court, with numerous small rooms at the north and south sides and two others on the west. The rooms are used at the present day by the men of Bawitti when they come to gather the rice-crop at Ain el Haiss. It is not a little remarkable that no reference to this large structure is to be found in Cailliaud’s account; its position (some 300 metres only south-west of the sheikh’s tomb at Ain el Haiss) would seem to preclude the possibility of confusing it with the other ruins he describes. He gives however (_l.c._ p. 195) the latitude of El Haiss as 28° 0′ 32″,[69] “latitude du couvent chrétien,” from which it would appear likely that he considered this place a convent. There is no evidence to decide whether the building is of Roman or Coptic origin. Far more enduring and more important (in a modern sense) than any of their buildings, were the extensive excavations carried out by the Romans for the improvement of the water-supply of oasis. In the neighbourhood of Bawitti especially, long series of shafts sunk in the sandstones and clays which form the ground, are frequently to be seen. These shafts, which vary from 1 to 3 metres in diameter, are sometimes round, sometimes rectangular, and are placed at only short distances apart. They are connected below with long tunnels, along which flows the water from the springs. Cailliaud mentions the existence of ten of these ancient aqueducts near Mandisha, eight of which still conveyed water in 1820; he entered one and followed it for 40 metres. He counted no less than fourteen shafts connected with this tunnel in a length of 150 metres, and records that one measured had a rectangular shape, 1·45 metres by 0·45 metres, and was perfectly cut in the rock, with footholds for the descent of the workmen. The largest aqueduct found by Cailliaud is south-west of El Qasr; its size is such that a man is able to walk in it. This tunnel, which now contains no water, leads from an excavation 5 metres in diameter by 8 metres deep, and in a length of 55 metres it is entered by ten shafts. In the same neighbourhood Cailliaud counted more than thirty other aqueducts, mostly coming from the south, like those of Mandisha. Four of these discharge their water into a huge excavation 70 metres diameter and 12 metres deep. The only example of an underground aqueduct at present known to exist in the south part of the oasis is one discovered by Ascherson a few kilometres east of Ain el Haiss; it is at present dry.