Behind this monument, towards the north, may be seen a small bridge of three arches, spanning the bed of a watercourse. To the south-west of the citadel are the remains of a theatre, and to the south-east of it two very magnificent reservoirs, the northern one intended to contain rain-water, but that to the south was supplied from a well at some little distance, between which and the reservoir are the remains of a solidly constructed aqueduct. Perhaps the most remarkable of the ruins is one due east of the citadel; it must have been a building of immense size, but it is impossible from its present appearance to form any conjecture as to its original destination. The walls, which were built of rubble masonry, of great thickness, have been rent asunder into huge masses, too large to have been moved by any mere mechanical power likely to have been employed, and yet they lie scattered about, without any apparent order, in every direction. In the midst of these huge masses, confusedly hurled together, we observed a small opening, through which it was just possible to crawl, giving entrance to a series of reservoirs of immense height and size, separated by partitions, yet connected together by arched passages. The cistern by which we entered was about thirteen feet square, beyond it were two larger ones, 79 feet long by 13 broad. There were at least six others, deserving of a much closer examination than we had time to give to them. Semicircular recesses were made in the walls here and there to enable the water to be drawn easily from above. The masonry throughout was quite perfect, not a trace visible of any great convulsion of nature, which alone, one would think, could have effected the ruin of the superincumbent building. Twenty minutes more brought us from Oudena to the southern end of the plain spanned by the aqueduct, where is a domed building, from which the syphon of the modern aqueduct starts; this is sixteen miles from Tunis, and twenty-and-a-half from Zaghouan. From this spot we continued our journey through an undulating country overgrown with brushwood, and after a few miles arrived at the ruins of a Roman post, called by the Arabs Bab Khalid, the ancient name of which is unknown.[108] The gate, or small triumphal arch, which gives its name to the place, and which was entire when Guérin visited it in 1860, has now fallen; one half however remains upright. There are numerous cisterns and foundations of buildings scattered about, but nothing of much interest. At thirty-three miles from Tunis is the spot called Magaran, where the two sources from Zaghouan and Djougar unite, and are conveyed in a single stream to Tunis, as they formerly were to Carthage.