Frontinus's chief work is "De aquaeductu", in two books, an official report to the emperor on the state of the aqueducts of Rome. It presents a history and description of the water-supply of Rome, including the laws relating to its use and maintenance. He provides the history, sizes and discharge rates of all of the nine aqueducts of Rome at the time at which he was writing at the turn of the 1st century AD: the Aqua Marcia, Aqua Appia, Aqua Alsietina, Aqua Tepula, Anio Vetus, Anio Novus, Aqua Virgo, Aqua Claudia and Aqua Augusta. Frontinus describes the quality of water delivered by each, mainly depending on their source, be it river, lake, or spring.