But as even this permission opened a door for great abuses, from the fraudulent conduct of the aquarii, who damaged the ducts for the purpose of selling the aqua caduca, a remedy was sought by the institution of castella privata, and the public were henceforward forbidden to collect the aqua caduca, unless permission was given by special favor (beneficium) of the emperor. The right of water (jus aquce impetratce) did not follow the heir or purchaser of the property, but was renewed by grant upon every

change in the possession. Castella Domestica, leaden cisterns, which each person had at his own house to receive the water laid on from the castellum privatum. These were, of course, private property. The number of public and private castella in Rome at the time of Nerva, was 247. All the water which entered the castellum was measured, at its ingress and egress,

by the size of the tube through which it passed. The former was called modulus acceptoriuSj the latter erogatorius. To distribute the water was termed erogare ; the distribution, erogatio ; the size of the tube, fistularum or modulorum capacitus, or lumen. The smaller pipes which led from the main to the houses of private persons, were called

punctoe ; those inserted by fraud into the duct itself, or into the main after it had left the castellum, fistula, illicitce.

The erogatio was regulated by a tube called calix, of the diameter required, attached

22 PRELIMINARY ESSAY.

to the extremity of each pipe where it entered the castellum ; it was probably of lead in the time of Vitruvius, such only being mentioned by him but was made of bronze ;