"The souterasi," says Andreossy,
"are masses of masonry, having generally the form of a truncated pyramid
or an Egyptian obelisk. To form a conduit with souterasi, we choose
sources of water, the level of which is several feet higher than the
reservoir by which it is to be distributed over the city. We bring the
water from its sources in subterranean canals, slightly declining until
we come to the borders of a valley or broken ground. We there raise on
each side a souterasi, to which we adapt vertically leaden pipes of
determinate diameters, placed parallel to the two opposite sides of the
building. These pipes are disjoined at the upper part of the obelisk,
which forms a sort of basin, with which the pipes are connected. The one
permits the water to rise to the level from whence it had descended; by
the other, the water descends from this level to the foot of the
souterasi, where it enters another canal underground, which conducts it
to a second and to a third souterasi, where it rises and again descends,
as at the last station. Here a reservoir receives it and distributes it
in different directions by orifices of which the discharge is known."
Again he says, "it requires but little attention to perceive that this
system of conducting tubes is nothing but a series of siphons open at
their upper part, and communicating with each other. The expense of a
conduit by souterasi is estimated at only one-fifth of that of an
aqueduct with arcades." There seems to be really no advantage in these
pyramids, further than as they serve the purpose of discharging the air
which collects in the pipes. They are in themselves an evident
obstruction, and the water would flow more freely without any
interruption of the kind. In regard to the leaden pipes, again, they
would have required, with so little head pressure as is stated, to be
used of very extraordinary dimensions to pass the same quantity of water
as was discharged along the arched conduits (see also works quoted under
CONSTANTINOPLE). The other principal source from which Constantinople is
supplied, is from the high grounds 6 or 8 m. west of the town, from
which it is conducted by conduits and arches, in the same manner as the
others. The supply drawn from all these sources, as detailed by
Andreossy, amounted to 400,000 cubic ft. per day.
(A. S. M.; J. M. M.)

Aqueducts and water supply.

III. _Modern Construction._--Where towns are favourably situated the
aqueduct ma