The Cisterns of Tawila, or the Tawila Tanks, are the best-known historic site in Aden, Yemen. The site consists of a series of tanks of varying shape and capacity. They are connected to one another and located in Wadi Tawila to the southwest of Adens oldest district, Crater. Originally there were about 53 tanks, but only 13 remain following a succession of renovations, including those done by the British in the 19th century.
The existing tanks have a combined capacity of about nineteen million gallons. The tanks were designed to collect and store the rain that flows down from the Shamsan massif through Wadi Tawila, and to protect the city from periodic flooding. The largest of the tanks are the Coghlan Tank at the center of the main site and the large, circular Playfair Tank, located at the lowest point, outside the main site. The tanks were hewn from the volcanic rocks of Wadi Tawila and then lined with a special stucco that included volcanic ash to create a strong, natural cement that rendered the tanks walls impermeable in order to retain water for extended periods.
Visitors to the Tanks are often surprised by the words on a plaque near the Coghlan Tank: Regarding the original construction of which nothing is accurately known There is indeed little hard evidence and there are few reliable sources of information about the Tanks. One favored hypothesis is that Himyar, a pre-Islamic Arabian kingdom that ruled parts of Yemen from 115 B.C. to 525 A.D., started to build water tanks in the area that eventually became the Cisterns of Tawila. The Himyarites are known to have employed water-catchment tanks in other areas under their rule.
The proposed Himyaritic origins of the tanks may help explain a recessed, rectangular area in the Coghlan tank that, according to the Director of the site, could have been used in pre-Islamic times for animal sacrifice. The Tanks were mentioned in some manuscripts after the coming of Islam to Yemen in the 7th century A.D. Aden has Tanks that store water when the rain falls, wrote Al-Hamadani in the 10th century.Al-Makdsi, writing three centuries later, also recorded the presence of wells and cisterns in Aden.
By the time of the Rassulid dynasty (1229-1454 A.D.), the Tanks had fallen into disrepair. However, the Rassulids recognized the utility of the Tanks and began to restore them. This restoration has led some to claim that the Rassulids built the Tanks, thereby obscuring what are, in all probability, the far more ancient origins of the Tanks. After the Rassulids, the Tanks once again fell into disrepair, damaged by flooding and neglect and filled with the rubble of successive floods.