Discoveries made during work to modernize Line B of the Rome underground, together with research in the historical archive of the Archaeological Superintendency of Rome, have added to knowledge of ancient topography of the area between the modern roads viale Manzoni, via Statilia and via Emanuele Filiberto. In antiquity, this area situated between the southern slopes of the Esquiline hill and the north-eastern slopes of the Caelian, was crossed by the _via Caelimontana_ and its branches, as well as by the Neronian aqueduct, which entered Rome at Porta Maggiore. In via Emanuele Filiberto, behind the Scala Santa, the work brought to light a number of stretches of one of these branches, situated in a small valley which sloped strongly from north to south, associated with an imposing sewer system. The latter, of imperial date, continued in use, with successive restorations, until a late period. On the Esquiline side, along another ancient road, retraced by the present viale Manzoni - via di S. Quintino, which from the Colosseum valley led to Porta Maggiore, the remains of at least three buildings were uncovered. These finds confirmed the residential nature of the area from the early imperial period until the late empire. Further south, the remains of at least four rooms from another domus were found. This structure was obliterated between the end of the 1st century and the mid 2nd century A.D. by the construction of an imposing structure in _opus mixtum_, corresponding perhaps to a stretch of the northern perimeter of the _Castra Priora Equitum Singularium_, the Trajanic garrison for the emperor’s personal guard. This cavalry troop was disbanded by Constantine who razed the Castra Nova to the ground in order to build the Lateran Basilica, whilst a late antique road crossed the place once occupied by the _Castra Priora_.