Various causes of dilapidation are enumerated by our author ; the cupidity of individuals through whose lands the aqueducts passed, and who, for the sake of irrigation, or for domestic uses, were tempted to enlarge any holes through which the water (Aqua Caduca) oozed out ; the violence of tempests, the imperfection of the work, especially in the more modern structures, and the softness of the material, tuffa, too frequently employed in portions of the mason work, where there was great pressure. The arcades, and especially those which traversed streams, were particularly liable to damage from the violence of storms.

Another considerable source of repair, arose from the adhesion of the sediment to the sides and bottom of the water-channels, forming a thick, hard crust, which materially obstructed the passage of the water, and by eventually raising its level, occasioned breaks in the channel, whence the waters escaping, not only destroyed it, but the sub-structures of

every kind in the vicinity.* All work of repair, was however, as much as possible suspended in the summer season, as then the free use of the water was most needed and agreeable.t The spring and autumn were the working periods. Moreover, a moderate temperature was deemed advantageous, as permitting the masonry to be laid with the degree of humidity deemed essential to its perfection and ultimate solidity, excessive heat and cold being alike unfavorable

to such a result. Above all, it was a rule, before beginning any reparation, to provide on the spot, every thing that could be required, and in sufficient quantity to ensure a rapid execution.