In many other places besides Rome, part of the amphitheatre was at times filled with water for the exhibition of naval fights, indeed the actual remains of the conduit for the water are shewn in more than one place. At Verona, where the area of the amphitheatre is considerably below the level of the adjacent ground, the conduit or _specus_ is shewn at the level of the second gallery, and below that of the upper one, and the water seems to have gone down a cascade into the end of a corridor or passage at the lowest level. At Capua the aqueduct for bringing in the water and a large drain for carrying it off rapidly, are shewn, both at a low level[79]. In either of these cases, the substructure is to a great extent filled up with vaulted brick chambers separated by passages, but the walls and vaults are lined with that peculiar cement that resists water, and thus a great part of the surface may have been covered with water to a sufficient depth for the purpose. At Puteoli or Pozzuoli, near Naples, the underground chambers of the amphitheatre are unusually perfect, and the brick floor over them, with numerous trap-doors, with deep grooves round the edge for a cover to fit tight over them when the surface was flooded[80]; at Tusculum one of the canals has been excavated, the other is still buried. From these it appears that the naval fights were represented as in a river, rather than in the sea. There are two long straight passages, the whole length of the central space, with no doors in them; and the walls are faced with the peculiar water-cement. These passages are wide enough for a trireme to pass along, and it seems more probable that the naval fight took place on this sort of river than on the whole surface, which would have been necessary for a sea-fight. This obviously applies equally to the Colosseum, where the great excavations in 1875 shewed that there were _two_ canals on each side of a great central passage, parallel to it and to each other, with an interval of about six feet between them, which was flooded when the water was let in to make two fine sheets of water the whole length of the arena, each about three hundred feet long and fifty feet wide[81]. These were just under the boards, which were carried away and placed on the corbels provided for them in front of the _podium_, but below the level of the base of it. The walls to support this body of water are unusually thick, and have buttresses on both sides for greater strength[82]. The two canals were not of the same width, but of the same depth, ten feet, with passages, ten feet high, under them. The most narrow canal is nearest to the centre, and has been supported on great beams of wood resting upon the massive walls; the places for the ends of the beams are left at short intervals in the walls. The other and wider canal had brick arches to support it, which remain, though the great leaden cistern in the form of a canal has been destroyed.