This is a gigantic piece of hydraulic engineering built by the Arab invaders of the 10th century. As is well known, they often used Hammams, so the need for a water supply was not only for common use, for the population and for field irrigation. The ancient Arabic technology made use of a careful study of the ground and groundwater sources and of the sheer strength of powerful and willing arm-power. This latter dug several levels of underground channels through Palermo so that the water could reach the surface and wells of the traditional fortified courtyards and suburban villages. Today there are three levels of channels that can be visited together with expert speleologists.