which these two lower compartments should be cleaned out from time to
time. The specus or channel itself was, of course, constructed of
masonry, generally of blocks of stone cemented together, and it was
frequently, though not, it would appear always, lined with cement inside.
It was roofed over, and ventilating shafts were constructed at intervals;
in order to encourage the aeration of the water, irregularities were
occasionally introduced in the bed of the channel. The water supplied by
the different aqueducts was of various qualities; thus, for instance,
that of the Alsietine, which was taken from a lake about 18 miles from
Rome, was of an inferior quality, and was chiefly used to supply a large
naumachia, or reservoir, in which imitation sea fights were performed;
while, on the other hand, the water of the Marcian was very clear and
good, and was therefore used for domestic purposes. Frontinus gives the
most accurate details as to the measurements of the amount of water
supplied by the various aqueducts, and the quantities used for different
purposes. From these details Mr. Parker computes the sectional area of
the water at about 120 square feet, and says: "We can form some opinion
of the vast quantity if we picture to ourselves a stream 20 ft. wide by 6
ft. deep constantly pouring into Rome at a fall six times as rapid as
that of the river Thames." He considers that the amount was equivalent to
about 332 million gallons a day, or 332 gallons per head per day,
assuming the population of the city to be a million. When we consider
that we in London have only 30 gallons a head daily, and that many other
towns have less, we get some idea of the profusion with which water was
supplied to ancient Rome. But the remains of Roman aqueducts are not only
to be found near Rome. Almost every Roman city, whether in Italy or in
the south of France, or along the north coast of Africa, can show the
remains of its aqueduct, and almost the only things that are to be seen
on the site of Carthage are the remains of the Roman water tanks and the
ruins of the aqueduct which supplied them. The most beautiful aqueduct