eat importance. The line of the aqueducts was marked by _cippi_,
inscribed (in the case of the Anio Vetus, Marcia, Tepula, Julia and
Virgo--those of the Claudia and Anio Novus are uninscribed, and those of
the Traiana are differently worded) with the name of the aqueduct, the
distance from the next _cippus_ (generally 240 ft.) and the number,
counting from Rome (not from the springs). These boundary stones were
erected in pairs, to mark off the strip of land 30 ft. in width reserved
for the aqueduct, and for the road or path which generally followed it.
The shafts (_putei_) often stood, but not necessarily, at the same
points as the _cippi_.

To these nine must be added the two following, constructed after
Frontinus's time: (10) AQUA TRAIANA, from springs to the north-west of
the Lacus Sabatinus (Lago di Bracciano), constructed by Trajan in A.D.
109, about 36-1/2 English miles in length. It was restored by Paul V. in
1611, who made use of and largely transformed the remains of the ancient
aqueduct; he allowed some of the inferior water of the lake to flow into
the channel, and it is thus no longer used for drinking. (11) AQUA
ALEXANDRINA, rising about 14 English miles from Rome, between the Via
Praenestina and the Via Labicana, the work of Alexander Severus (A.D.
226). The springs now supply the modern Acqua Felice, constructed by
Sixtus V. in 1585, but the course of the latter is mainly subterranean
and not identical with that of the former.

[Illustration: PLATE I.

_Photo, Altnari._
AQUA CLAUDIA, ROME.

_Photo, Neurdein._
PONT DU CARD, NIMES (NEMAUSUS).]

[Illustration: PLATE II.

_Photo, Laureat y Cia._
ROMAN AQUEDUCT AT SEGOVIA.

AQUEDUCT OF ROQUEFAVOUR, MARSEILLES.
Early nineteenth century.

_Photo, Brogi._
PISCINA MIRABILIS AT BAIAE.

_Photo, Dr T. Ashby._
AQUA MARCIA, ROME.]

It is agreed that these eleven are all that were constructed. Procopius
speaks of fourteen (and the Regionary catalogues mention others), but
this number includes branch conduits. All the aqueducts ended in the
city in huge _castella_ or reservoirs for the purpose of distribution.
Vitruvius recommends the division of these into three parts--one for the
supply of fountains, &c., one for the public baths and one for private
consumers. In the Piazza Vittorio Emmanuele at Rome there are still to
be seen the remains of a large ornamental fountain built probably for
the Aqua Julia by Domitian or Alexander