Lead was universally used for the supply-pipes from the castella, and notwithstandof health, we find in ing Vitruvius speaks of this metal as objectionable on the score Frontimis no allusion to any evil from its general employment.

The liability of these gigantic works to injury and decay, especially in the portions above ground, is forcibly dwelt upon by Frontinus. The subterranean parts were easily kept in order, as they were neither subject to the action of frost, nor to the action of the

summer's heat, which the Romans seem to have considered hardly less injurious to mason work. 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