[Footnote: An address by Prof. W.H. Corfield, M.D., M.A., delivered
before the Sanitary Institute of Great Britain, July 9, 1885.--_Building
News_.]
As the supply of water to large populations is one of the most important
subjects in connection with sanitary matters, and one upon which the
health of the populations to a very large extent depends, I propose to
give a short account of some of the more important works carried out for
this purpose by the ancient Romans--the great sanitary engineers of
antiquity--more especially as I have had exceptional opportunities of
examining many of those great works in Italy, in France, and along the
north coast of Africa. Of the aqueducts constructed for the supply of
Rome itself we have an excellent detailed account in the work of
Frontinus, who was the controller of the aqueducts under the emperor
Nerva, and who wrote his admirable work on them about A.D. 97.
It may be interesting in passing to mention that Frontinus was a
patrician, who had commanded with distinction in Britain under the
emperor Vespasian, before he was appointed by the emperor Nerva as
controller (or, we should say, surveyor) of the aqueducts. He was also an
antiquarian, and in his work he not only describes the aqueducts as they
were in this time, but also gives a very interesting history of them. He
begins by telling us that for 441 years after the building of the
city--that is to say, B.C. 312--there was no systematic supply of water
to the city; that the water was got direct from the Tiber, from shallow
wells, and from natural springs; but that these sources were found no
longer to be sufficient, and the construction of the first aqueduct was
undertaken during the consulship of Appius Claudius Crassus, from whom it
took the name of the Appian aqueduct. This was, as may be expected from
its being the first aqueduct, not a very long one; the source was about
eight miles to the east of Rome, and the length of the aqueduct itself
rather more than eleven miles, according to Mr. James Parker, to whose
paper on the "Water Supply of Ancient Rome" I am indebted for many of the
facts concerning the aqueducts of Rome itself. This aqueduct was carried
underground throughout its whole length, winding round the heads of the
valleys in its course, and not crossing them, supported on arches, after
the manner of more recent constructions; it was thus invisible until it
got inside the city itself, a very important matter when we consider how
liable Rome was, in these early times, to hostile attacks.
It was soon found that more water was required than was brought by this
aqueduct, and it was no doubt considered desirable to have tanks at a
higher level in the city than those supplied by the Appian aqueduct. It
was determined, therefore, to bring water from a greater height, and from
a greater distance, and the river Anio, above the falls at Tivoli, was
selected for this purpose. The second aqueduct, the Anio Vetus, was no
less than 42 miles in length, and was, like the Appian, entirely under
the surface of the ground, except at its entrance into Rome at a point
about 60 ft. higher than the level of the Appian aqueduct.
Little search has been made for the remains of this aqueduct, and its
exact course is not known; but during my examination of the remains of
the subsequent aqueducts at a place called the Porta Furba, near Rome,
where the ruins of five aqueducts are seen together, and at, or close to,
which point the Anio Vetus must also have passed underground, I was
rewarded for my search by discovering a hole, something like a fox's
hole, leading into the ground; and on clearing away a few loose stones
which had apparently been thrown into it, and putting my arm in, I found
that it led into the specus or channel of an underground aqueduct; and on
relating this incident to the late Mr. John Henry Parker, the
antiquarian, who was then in Rome, and showing him a sketch of the place,
he said that he had no doubt that I had been fortunate enough to discover
the exact position of the veritable Anio Vetus at that spot. These two
aqueducts sufficed for the supply of Rome with water for about 120 years,
for Frontinus tells us that 127 years after the date at which the
construction of the Anio Vetus was undertaken--that is to say, the 608th
year after the foundation of the city--the increase of the city
necessitated a more ample supply of water, and it was determined to bring
it from a still greater distance. It was no longer considered necessary
to conceal the aqueduct underground during the whole of its course, and
so it was in part carried above ground on embankments or supported upon
arches of masonry. The water was brought from some pools in one of the
valleys on the eastern side of the Anio, some miles farther up than the
point from which the Anio Vetus was supplied; and the new aqueduct, which
was 54 miles in length, was called the Marcian, after the Prætor Marcius,
to whom the work was intrusted. Frontinus also tells us the history of
the other six aqueducts which were in existence in his time, viz., the
Tepulan, the Julian, the Virgo, the Alsietine or Augustan, the Claudian,
and the Anio Novus; the last two being commenced by the Emperor Caligula,
and finished by Claudius, because "seven aqueducts seemed scarcely
sufficient for public purposes and private amusements;" but it is not
necessary for our purpose to give any detailed account of the course of
these aqueducts; it is only necessary to mention one or two very
interesting points in connection with them. In order to allow of the
deposit of suspended matters, piscinæ, or settling reservoirs, were
constructed in a very ingenious manner. Each had four compartments, two
upper and two lower; the water was conducted into one of the upper
compartments, and from this passed, probably by what we should call a
standing waste or overflow pipe, into the one below; from this it passed
(probably through a grating) into the third compartment at the same
level, and thence rose through a hole in the roof of this compartment
into the fourth, which was above it, and in which the water, of course,
attained the same level as in the first compartment, thence passing on
along the aqueduct, having deposited a good deal of its suspended matter
in the two lower compartments of the piscinæ. Arrangements were made by
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
bridge in the world, on the course of the aqueduct which supplied the
ancient Nemaucus, now Nismes, still stands, and is called, from the name
of the department in which it is, the Pont du Gard. It consists of a row
of large arches crossing the valley over which the water had to be
carried, surmounted by a series of smaller arches, and these again by a
series of still smaller ones, carrying the specus of the aqueduct. This
splendid bridge still stands perfect, so that one can walk through the
channel along which the water flowed, and it might be again used for its
original purpose. There was, however, one city which, from the fact that
a great part of it was situated upon a hill, was more difficult to supply
with water than any of the rest, and which, at the same time, from its
size, its great importance, and the fact that it was the favorite summer
residence of several of the Roman emperors, and notably of Claudius, who
was born there, and who had a palace on the top of the hill, must of
necessity be supplied with plenty of water, and that too from a
considerable height. I refer to Ludgunum (now Lyons), then the capital of
Southern Gaul. This city was built by Lucius Munatius Plaucus, by order
of the Senate in A.U.C. 711. Augustus went there in A.U.C. 738, and
afterward lived there from 741 to 744. It was he who raised it to a very
high rank among Roman cities. It had its forum near the top of the hill
now called Fourvieres (probably a corruption of Forum Vetus), an imperial
place on the summit of the same hill, public baths, an amphitheater, a
circus, and temples.
In order to supply this city with water, standing as it did on the side
of a hill at the junction of two great rivers (now Rhone and Saone), it
was necessary to search for a source at a sufficient height, and this
Plaucus found in the hills of Mont d'Or, near Lyons, where a plentiful
supply of water was found at a sufficient height, viz., that of nearly
2,000 ft. above the sea. From this point an aqueduct, sometimes called
from its source the aqueduct of Mont d'Or, and sometimes the aqueduct of
Ecully, from the name of a large plain which it crossed, was constructed,
or rather two subterranean aqueducts were made and joined together into
one, which crossed the plain of Ecully, in a straight line still
underground; but the ground around Lyons was not like the Campagna, near
Rome, and it was necessary to cross the broad and deep valley now called
La Grange, Blanche. This, however, did not daunt the Roman engineers;
making the aqueduct end in a reservoir on one side of the valley, they
carried the water down into the valley, probably by means of lead pipes,
in the manner which will be described more at length further on, across
the stream at the bottom of the valley by means of an aqueduct bridge 650
ft. long, 75 ft. high, and 28½ ft. broad, and up the other side into
another reservoir, from which the aqueduct was continued along the top of
a long series of arches to the reservoir in the city, after a course of
about ten miles.
In the time of Augustus, however, it was found that the water brought by
this aqueduct was not sufficient, especially in summer; and as there was
a large Roman camp which also required to be supplied with water,
situated at a short distance from the city, it was determined to
construct a second aqueduct. For this purpose the springs at the head of
a small river, called now the Brevenne, were tapped, and conveyed by
means of an underground aqueduct (known as the aqueduct of the Brevenne)
which wound round the heads of the valleys, and after a course of about
thirty miles is believed by some to have arrived at the city, but by
others to have stopped at the Roman camp, and to have been constructed
exclusively for its supply.
I have here a diagram, after Flacheron, showing a section of this
aqueduct, and this will give a very good general idea of the section of a
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
the aqueduct at various parts of its course show clearly enough. It
commences, as I have said, about a mile and a half from the present St.
Chamond, a town on the river Gier, about 16 miles from St. Etienne. Here
a dam appears to have been constructed across the bed of the river,
forming a lake from which the water entered the channel of the aqueduct,
which passed along underground until it came to a small stream which it
crossed by a bridge, long since destroyed.
After this it again became subterraneous for a time, and then crossed
another stream on a bridge of nine arches, the ruins of some of the
columns of which are still to be seen; and from these ruins it would
appear that the bridge had, at some time or another, been destroyed,
probably by the stream running under it having become torrential, and
subsequently rebuilt; again it became concealed underground, to reappear
in crossing a small valley and another small stream, when it was again
concealed by the ground, and in one or two places channels were even cut
for it through the solid rock, after which it reappeared on the surface
at a point where now stands the village of Terre-Noire, and where it was
necessary that it should somehow or another cross a broad and deep
valley. It ended in a stone reservoir, from which eight lead pipes
descending into the valley were carried across the stream at the bottom
on an aqueduct bridge, about 25 ft. wide, and supported by twelve or
thirteen arches, and then mounted the other side of the valley into
another reservoir, of which scarcely any remains are now seen, from which
the aqueduct started again, disappearing almost immediately under the
surface of the ground, to appear again from time to time crossing similar
valleys and streams upon bridges, the remains of some of which may still
be seen, until it reached Soucieu, on the edge of the valley of the
Garonne, where are still seen the remains of a splendid bridge, the
thirteenth on its course, nearly 1,600 ft. long, and attaining a height
of 56 ft. at its highest point above the ground. The object of this
bridge was to convey the channel of the aqueduct at a sufficient height
into a reservoir on the edge of the valley.
The remains of this bridge leave no doubt that it was purposely destroyed
by barbarians; some of the arches near the end of it remain, while the
rest have been thrown down, some on one side and some on the other; but
happily the arches next to the reservoir, at the end of the bridge and on
the edge of the valley, remain, and the reservoir itself is still in part
intact, supported on a huge mass of masonry. Four holes are to be seen in
that part of the front of the reservoir which is left, being the holes
from which the lead pipes descended into the valley. There must have been
nine of these pipes in all. These holes are elliptical in shape, being 12
in. high by 9½ in. wide, and the interior of the reservoir is still seen
to be covered with cement. The walls of the reservoir were about 2 ft. 7
in. thick, and were strengthened by ties of iron; it had an arched stone
roof in which there was an opening for access. From this the nine lead
pipes descended the side of the valley supported on a construction of
masonry, crossed the river by an aqueduct bridge, and ascended into
another reservoir on the other side, entering the reservoir at its upper
part just below the spring of the arches of the roof. From this reservoir
the aqueduct passed to the next on the edge of the large and deep valley
of Bonnan, being underground twice and having three bridges on its
course, the last of which, the sixteenth on the course of the aqueduct,
ends in a reservoir on the edge of the valley. Only one of the openings
by which the siphons, of which there were probably ten, started from the
reservoir is now left. The bridge across the valley below had thirty
arches, and was about 880 ft. long by 24 ft. wide.
A number of the arches still remain standing, and, the pillars of the
arches were constructed of transverse arches themselves. The work
consisted of concrete, formed with Roman cement so hard that it turns the
points of pickaxes when employed against it, with layers of tiles at
regular intervals. The surface of the concrete is covered with small
cubical blocks of stone placed so that their diagonals are horizontal and
vertical, and forming what is known as _opus reticulatum_. After crossing
the bridge the pipes were carried up the other side of the valley into a
reservoir, of which little remains, and then the aqueduct was continued
to the next valley, passing over three bridges in its course. This
valley, that of St. Irenée, is much smaller than either of the others,
but nevertheless it was deep enough to necessitate the construction of
inverted siphons, of which there were eight. Leaving the reservoir on the
other side of this valley, the aqueduct was carried on a long bridge (the
twentieth on its course) which crossed the plateau on the top of
Fourvieres and opened into a large reservoir, the remains of which are
still to be seen on the top of that hill.
From this reservoir, which was 77 ft. long and 51 ft. wide, pipes of lead
conveyed the water to the imperial palace and to the other buildings near
the top of the hill. Some of these lead pipes were found in a vineyard
near the top of Fourvieres at the beginning of the eighteenth century,
and were described by Colonia in his history of Lyons. They are made of
thick sheet lead rolled round so as to form a tube, with the edges of the
sheet turned upward, and applied to one another in such a way as to leave
a small space, which was probably filled with some kind of cement. These
pipes, of which it is said that twenty or thirty, each from 15 ft. to 20
ft. long, were found, were marked with the initial letters TI. CL. CAES.
(Tiberius Claudius Cæsar), and afford positive evidence that the work was
carried out under the emperor Claudius. Lead pipes, constructed in a
similar manner, have also been found at Bath, in this country, in
connection with the Roman baths. The great difference between this
aqueduct and those near Rome arises from the fact that, instead of being
carried across a nearly flat country, it was carried across one
intersected with deep ravines, and that it was therefore necessary to
have recourse to the system of inverted siphons. There can be no doubt
that the inverted siphons were made of lead, although no remains of them
have been found; for we know that the Romans used lead largely, and, as
we have seen, pieces of the lead distribution pipes have been found. It
is possible, and even likely, that strong cords of hemp were wound round
the pipes forming the siphons, as is related by Delorme in describing a
similar Roman aqueduct siphon near Constantinople; Delorme also
describes, in the aqueduct last mentioned, a pipe for the escape of air
from the lowest part of the siphon carried up against a tower, which was
higher than the aqueduct, and it is certain that there must have been
some such contrivance on the siphons of the aqueduct constructed at
Lyons.
Flacheron supposes that they consisted of small pipes carried from the
lowest part of the siphons up along the side of the valley and above the
reservoirs, or, in some instances, of taps fixed at the lowest part of
the siphons. The Romans have been blamed for not using inverted siphons
in the aqueducts at Rome, and it has been said that this is a sufficient
proof that they did not understand the simplest principles of hydraulics,
but the remains of the aqueducts at Lyons negative this assumption
altogether. The Romans were not so foolish as to construct underground
siphons, many miles long, for the supply of Rome; but where it was
necessary to construct them for the purpose of crossing deep valleys,
they did so. The same emperor Claudius who built the aqueduct at Rome
known by his name built the aqueduct of Mont Pila, at Lyons, and it is
quite clear, therefore, that his engineers were practically well
acquainted with the principles of hydraulics. It is thus seen that the
ancient Romans spared no pains to obtain a supply of pure water for their
cities, and I think it is high time that we followed their example, and
went to the trouble and expense of obtaining drinking water from
unimpeachable sources, instead of, as is too often the case, taking
water which we know perfectly well has been polluted, and then attempting
to purify it for domestic purposes.
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