Roman aqueduct where constructed underground. It will be seen that the
specus or channel is 60 centimeters (or nearly 2 ft.) wide, and 1m. 57c.
(or a little over 5 ft.) high, and that it is lined with a layer of 3 c.
(or nearly 1¼ in.) of cement. It is constructed of quadrangular blocks of
stone cemented together, and has an arched stone roof. It will be noticed
also that the angles at the lower part of the channel are filled up with
cement; it appears also that this aqueduct crossed a small valley by
means of inverted siphons. But neither of these aqueducts came from a
source sufficiently high to supply the imperial palace on the top of
Fourvieres.

Their sources are, in fact, according to Flacheron, at a height of nearly
50 ft. below the summit of Fourvieres, and it was, therefore, considered
necessary by the emperor Claudius to construct a third aqueduct. The
sources of the stream now called the Gier, at the foot of Mont Pila,
about a mile and a half above St. Chamond, were chosen for this purpose,
and from this point to the summit of Fourvieres was constructed by far
the most remarkable aqueduct of ancient times, an engineering work which,
as will be seen from the following description, partly taken from
Montfalcon's history of Lyons, partly from Flacheron's account of this
aqueduct, and partly from my own observations on the spot, reflects the
greatest possible credit on the Roman engineers, and shows that they were
not, as has been frequently supposed by those who have only examined
aqueducts at Rome, by any means ignorant of the elementary principles of
hydraulics.

To tap the sources of a river at a point over 50 miles from the city, and
to bring the water across a most irregular country, crossing ten or
twelve valleys, one being over 300 ft. deep, and about two-thirds of a
mile in width, was no easy task; but that it was performed the remains of