The dam of Mareb was built probably some 1700 years B.C. by Lokman the Adite, though some authorities attribute its construction to Abd esh-shems, father of Himyar, founder of the Himyaric dynasty, and great-grandson of Kahtan—Joktan of the Hebrew Scriptures. Monsieur d’Arnaud, who visited Saba in 1843, describes the ruins of the dam. He says that it consisted of an enormous wall, two miles long and one hundred and seventy-five paces wide, connecting two hills. Dikes allowed the water to escape for the irrigation of the plain below. These openings are at different levels, so as to render practicable a supply of water at whatever height the contents of the reservoir might stand. The destruction of this great work took place probably about a hundred years after the birth of Christ; but although the catastrophe is referred to in the Koran, no certain date can be affixed to its occurrence. The fact that it stood the enormous pressure of water which must have constantly been present for some seventeen hundred years, testifies to the immensity and solidity of its construction. The tanks at Aden cannot, of course, compare with the dam of Mareb, yet they are in their way colossal undertakings, and the labour and time expended in their construction must have been enormous. They number about fifty altogether, and if in working order, would be capable of holding upwards of thirty million gallons. We know that at the time of the invasion of Raïs Suleiman in 1538, the inhabitants of Aden were entirely dependent upon these great cisterns for their water-supply. On Captain Haines visiting Aden in 1835, he found several of the tanks in use, but many were filled up with the _debris_ that the torrents had washed from the mountains above. In 1856 the restoration of the tanks was commenced, and now thirteen are in working order, capable of holding nearly eight million gallons of water. Their site is well chosen. They lie above the town, immediately under the high rocks that form the foot of Jibel Sham-sham, and in such a position that all the drainage of the rain-water is accumulated into channels, and poured into the succession of cisterns that lie one above another. The tanks are formed in various ways: some are cut into the solid bed of the rock, which is covered with a hard polished cement; others are dams built across the ravine; while a third variety of shape is formed by angles in the precipices being made use of, two of the walls of the cistern perhaps being the natural stone, and the others formed of masonry. The upper tanks are the first filled, the lower for the most part being supplied from the overflow of those above. In spite of the enormous space to contain the water and the slight rainfall of Aden, a series of heavy showers will not only fill the tanks, but cause an overflow stream of such bulk that very considerable damage has at times been caused by it, as it poured along its channel through the town to the sea.