g the buttresses. From
Gallicano onwards the course of these four aqueducts follows the lower
slopes of the Alban Hills. Previous writers on the subject have been
unable to determine their course, which is largely subterranean; but it
can be followed step by step with the indications given by the presence
of the calcareous deposit which was thrown out at the _putei_ or shafts
(which were, as a rule, placed at intervals of 240 ft., as were the
_cippi_) when the _specus_ was cleaned; and remains of bridges, though
less important, owing to the less difficult character of the country,
are not entirely absent (cf. the works by T. Ashby cited in
bibliography).[4] Near the 7th milestone of the Via Latina at Le
Capanelle, the Aqua Claudia and Anio Novus emerge from their underground
course, and run into Rome upon the long series of arches already
mentioned, passing over the Porta Maggiore. The Claudia sent off an
important branch from the Porta Maggiore over the Caclian to the
Palatine, but the main aqueduct soon reached its termination. A mile
farther on the Aqua Marcia also, owing to the gradual slope of the
ground towards Rome, begins to be supported on arches, which were also
used to carry the Aqua Tepula and the Aqua Julia (of the two latter,
before their junction with the Marcia, no remains exist above ground,
but inscribed _cippi_ of the last named and its underground channel have
been found at Le Capanelle, and _cippi_ also close to its springs, which
are a little way above Grottaferrata at Gli Squarciarelli). The Anio
Vetus followed the same line, but kept underground (as was natural at
the early period at which it was constructed) until the immediate
neighbourhood of Rome, near the locality known as "ad Spem veterem"
(from a temple of Spes, of which no remains are known) close to the
Porta Maggiore. At this point, besides the aqueducts named, the Aqua
Appia, as we are told by Frontinus, entered the city, and received an
important branch, the Appia Augusta. No remains of either have been
discovered outside the city.

The Aqua Alexandrina must also have entered the city here, though its
channel, which lay at some depth below ground, has not been discovered.
Considerable remains of its brick aqueducts exist in the district
between the Via Praenestina and the Via Labicana.

Of the two aqueducts on the right bank of the Tiber, the Alsietina, as
we have said, has no remains at all, while those of the Traiana are not
of gr