M.)

Roman.

In comparing Greek and Roman aqueducts, many writers have enlarged on
the greatness of the latter as an example of Roman contempt for natural
obstacles, or even of Roman ignorance of the laws of nature. Now, in the
first place, the Romans were not unacquainted with the law that water
finds its own level (see Pliny, _Hist. Nat._ xxxi. 57, "subit
altitudinem exortus sui"), and took full advantage of it in the
construction of lofty fountains and the supplying of the upper floors of
houses. That they built aqueducts across valleys in preference to
carrying pipes underground was due simply to economy. Pipes had to be
made of lead which was weak, or of bronze which was expensive; and the
Romans were not sufficiently expert in the casting of large pipes which
would stand a very great pressure to employ them for the whole course of
a great aqueduct. Secondly, the water was so extremely hard that it was
important that the channels should be readily accessible for repair as
well as for the detection of leakage.[1] Moreover, as we shall see, the
Roman aqueducts did not, in fact, preserve a straight line regardless of
the configuration of the country. A striking example is the aqueduct of
Nemausus (Nimes), the springs of which are some 10 m. from the town,
though the actual distance traversed is about 25. Other devices, such as
changing the level and then modifying the slope, and siphon arrangements
of various kinds, were adopted (as in the aqueduct at Aspendus).

Sextus Julius Frontinus, appointed _curator aquarum_ in A.D. 97,
mentions in his treatise _de aquaeductibus urbis Romae_ (on the
aqueducts of the city of Rome) nine aqueducts as being in use in his
time (the lengths of the aqueducts as given here follow his
measurements). These are: (1) AQUA APPIA, which took its rise between
the 6th and 7th milestones of the Via Collatina, and measured from its
source to the Porta Trigemina 11 Roman miles, of which all but about 300
ft. were below ground. It appears to have been the first important
enterprise of the kind at Rome, and was the work of the censor Appius
Claudius Caecus, from whom it derived its name. The date of its
construction was 312 B.C. (2) ANIO VETUS, constructed in 272-269 B.C. by
the censor Manius Curius Dentatus. From its source near Tivoli, on the
left side of the Anio, it flowed some 43 m.,[2] of which only 1100 ft.
was above ground. At the distance of 2 m. from Rome (Frontinus, i. 21),
it par