“Having dedicated the _Amphitheatre_, and having quickly completed the Thermæ hard by, he provided the most magnificent and expensive entertainment [for the people]. He exhibited a naval fight _in the old Naumachia_, and also a combat of gladiators; and, in one day also, five thousand wild beasts of all sorts[71].” Those _stagna_ were boarded over for the gladiators and for the wild beasts, but the boards could be moved and naval fights exhibited at other times, as had previously been done on the same spot in “the old Naumachia[72].” The account of the scenes that took place here, described by Dio Cassius, agrees with this. The excavations made in 1814 shewed that there were canals built of brick running parallel to each other the whole length of the area, as at Capua, and in several other amphitheatres; these were, no doubt, for the naval fights. The vessels were probably towed along from the opposite ends, and where they met were lashed together, and the sailors of one of them tried to board the other: to prevent this was the naval fight. Probably the space between these two canals was flooded when the water was let in. These canals, reservoirs, or _stagna_, were brought out more clearly in 1875, and the substructures which supported them were then made visible[73]. In the corridors are many remains of the open channels for the water brought from the aqueducts. They are not more than a foot deep, often not so much, being frequently much worn: when perfect they are nearly of that depth, and are lined with the peculiar cement used only for the aqueducts, called _Opus signinum_, and in Italian, _Coccio-pesto_. This is an invariable mark of an aqueduct; this open channel must have been brought across from the Cœlian reservoir on the colonnade, shewn upon the coin of Titus. The system of drainage for the rain-water is quite distinct from the channels for the aqueducts.