That of Trajan is chiefly subterranean, and has been described under the head of the Alseatina (VII.), but nearer Rome it is above ground, and is carried on an arcade against the wall of the Villa Pamphili-Doria, near the Porta di S. Pancratio. Both the arcade and the _specus_ are faced with the _opus reticulatum_ of that period. (664* is from a drawing, 1065 from nature.) In some parts, one side of the _specus_ has been cut away (1063). Just on the outside of that garden a large _castellum aquæ_ of this aqueduct has been made into a farm-house, and in the yard of that house a branch from it can be seen (665*), apparently for the purpose of irrigation; or, as some think, this was formerly the point of division, one branch going to the Vatican, the other to the great fountain on the Janiculum (960), above S. Pietro in Montorio. The division now takes place at a short distance from this point. Procopius, writing in the sixth century, admires the enormous quantity of water brought by this aqueduct to the highest point in Rome; as it descends the hill, it turns the wheels of the flour-mills. After it arrived at the low level of the ground in the Trastevere, the respirators of the pipes for this aqueduct are carried in tall pyramids resembling chimneys (540). Part of the arcade and _specus_ rebuilt by Paul V., near the garden before mentioned, is shewn in 1064, with the inscription of A.D. 1609 above it. XI. HADRIANA (?), TRAJANA (?) OR ALEXANDRINA (?). The next great work of the period of Trajan or of Hadrian, on the eastern side of Rome, was probably begun in the time of Trajan. It brought water from springs under Labicum, now La Colonna, the same that is now brought for the Aqua Felice. The water from several springs was collected in a central reservoir, on which an inscription of Hadrian was found by E. Q. Visconti in the eighteenth century. This is between Pantana and Gabii, in the valley under La Colonna (1540). There are several other reservoirs of the time of Trajan or Hadrian along the line (1637, 1638). This aqueduct was considered by Fabretti to be of the time of Alexander Severus, and since his time it has usually been called the Aqua Alexandrina. It may have been partly rebuilt and brought into use again in his time, after having been choked up with stalactite, one of the springs used proving to be a petrifying spring.