EMISSA´RIUM
EMISSA´RIUM (
ὑπόνομος), an artificial channel by which an outlet is formed to
carry off any stagnant body of water. (
Plin.
Nat. 33.75;
Cic. Fam. 16.1. 8）
Such channels may be either open or underground; but the most remarkable
works of the kind are of the latter description, as they carry off the
waters of lakes surrounded by hills. The skill of the ancients in tunnelling
has been already noticed under CRYPTA ; but long
before the art was applied to road-making, drainage-works on an immense
scale were employed to regulate the overflow of land-locked waters and to
prevent inundations. Thus in Greece, in the early times of the Minyae of
Orchomenus, we find the natural channels (katavóthra, as they are
now called) which carry off the waters of the Boeotian Cephisus through Lake
Copais to the sea, supplemented by two artificial emissaria or tunnels
(Müller,
Orchomenos2, 49 ff.). These are described, with a map of the surrounding
country, in
Dict. Geogr. 1.411: the longer of the two,
connecting the lake with the lower course of the Cephisus, is nearly four
miles in length according to Forchhammer (other accounts make it
considerably less, cf. Grote, pt. i. ch. 6, 1.114) and with about twenty
perpendicular shafts sunk into it, some of which are from 100 to 150 feet in
depth. The second tunnel, much shorter, unites the lakes Copais and Hylica,
running under the Acraephian plain at no great depth, and is likewise
provided with shafts. Both tunnels and shafts are now choked up, but can
still be traced. The natural katavóthra being insufficient to
carry off the waters of the Cephisus, much of what was once fertile alluvial
land is now turned to a swamp, and awaits the efforts of modern enterprise.
An abortive attempt to clear out these tunnels was made by an engineer named
Crates under the orders of Alexander the Great (
Strabo ix. p.407): it is announced (1888) that the reclamation
of Lake Copais is now to be again attempted.
Herodotus describes with marked interest the tunnel of Eupalinus at Samos, by
which a supply of fresh water was introduced into the city; and gives it the
first place among the “three greatest works of the Greeks,” the
others being the mole in the harbour of Samos and the Heraeon or temple of
Hera (3.60). These works unquestionably date from the tyranny of Polycrates,
the most flourishing period of Samos, which ended about B.C. 522; they are
mentioned by Herodotus in connexion with his reign, and Aristotle likewise
refers to
περὶ Σάμον ἔργα Ρολυκράτεια
(
Pol. 5.11 = p. 1313 b, 24). The mole still
exists, intact or at least restored; the Heraeon is represented by a single
column. This tunnel (
ὄρυγμα ἀμφίστομον,
Herod.
l.c.) had disappeared for centuries, and good
observers like Tournefort and Ross sought for it in vain. Within the last
few years it has been re-discovered by the Greek clergy on the spot, and to
a great extent cleared out at the expense of the principality; an account of
the excavations by G. Dennis appeared in the
Academy of Nov.
4, 1882, a much fuller one by E. Fabricius in the
Mittheilungen d.
deutsch. archäol. Inst. 9.165-191 (1884). The length of
the tunnel, given by Herodotus at seven stadia, probably does not exceed
1000 metres or
[p. 1.729]scarcely more than five stadia; it
is much choked by stalactites, and is not yet practicable throughout, but
has been explored for the length of 100 metres from the northern, 500 from
the southern extremity. The height and width are correctly estimated by
Herodotus at eight feet each; seven would be nearer the mark, though near
the ends it is wider. A deep and narrow channel (
ἄλλο ὄρυγμα) runs along it, three feet wide according to
Herodotus (really a little less), and thirty feet in depth: this applies
only to the southern end nearest the town, which was probably all that the
historian saw of it; elsewhere the depth is not so great. Along this the
water was conveyed; not however in the channel itself, but in earthenware
pipes, large numbers of which have been found in it; unless we are to
suppose that these are of later date. For the greater part of its course the
tunnel is hewn out of a hard limestone rock, on which the marks of the
chisel are still visible; towards the extremities the strata are softer, and
a lining of masonry was required. Niches occur at intervals, in some of
which lamps were found; and it is ventilated by about twenty shafts. An
interesting circumstance, as bearing upon the engineering skill of
Eupalinus, is that the tunnel was certainly pierced from both ends. The two
galleries did not, however, meet with the precision attained in modern
times; the floor of the upper one missed the roof of the lower by the space
of about a metre, and a cavern some twelve feet high had to be excavated,
marking the point of junction. The slope is easy and suitable for an
aqueduct, but the deep channel is probably an after-thought in consequence
of the right gradient not having been attained at once. This remarkable work
must have continued in use for many centuries, as traces of Roman and even,
it is said, of Byzantine constructions are found within it: full details on
these and other points will be found in the essay of Fabricius. On the other
hand, there is a second aqueduct, dating from Roman times, which follows the
outer circuit of the mountain; this would seem to show that the work of
Eupalinus was at one period abandoned.
1
A little later, probably, in date than the Samian aqueduct (about 480) were
the subterraneous channels constructed by Phaeax at Agrigentum in Sicily, to
drain the city; they were well worth seeing, says Diodorus (
11.25), for their magnitude, although in general
but little noticed. They are still called the
Condotti di
Feace, and adjoin the well-marked site of the huge reservoir
(
κολυμβήθρα,
piscina; not here, we think, a
“swimming-bath” ; it was full of fish and swans) mentioned
in the same passage by Diodorus, with which they were doubtless connected:
they are not yet excavated, but from their massiveness are probably in a
good state of preservation.
In Italy the Etruscans were the first great masters in the art of tunnelling,
and the Romans learnt it from them. They had an ample field for their
operations, as Central Italy abounds with intractable rivers, and
crater-lakes with no natural outlet. The Cloaca Maxima itself is quite as
much an emissary as a sewer, draining the Forum and Velabrum which
previously were swamps; the period to which it belongs, that of the last
kings, marks the culminating point of Etruscan civilisation at Rome. (On the
disputed question respecting the date, see
CLOACA) The celebrated emissary of the Alban Lake is
still in working order; it is probably of Etruscan origin, and older than
the Veientine war with which tradition connects it. The length is about
6,000 feet; for further details see
Dict. Geoqr. s. v.
Albanus Lacus. The neighbouring volcanic
lake of Nemi is drained in a similar manner; and remains exist to show that
the system was likewise applied to Trasimenus, a lake of quite different
geological formation, broad and shallow.
The greatest Roman work of this description is the emissary of lake Fucino,
rendered further
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Emissarium of lake Fucino.
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interesting by the mention of it in ancient authors and the
complete drainage of the lake in recent years. The
vitrea
Fucinus unda of Virgil (
Aen. 7.759) is now
altogether a thing of the past. Julius Caesar is said to have first
conceived the idea of this stupendous under-taking (
Suet. Jul. 44), which was carried into effect by the Emperor
Claudius (
Tac. Ann. 12.57). The length of
the emissary, which lies nearly in a direct line from the lake to the river
Liris (Garigliano), is 15,600 English feet, or three miles all but 80 yards.
The number of workmen employed was 30,000, and the time occupied in the work
eleven years. (
Suet. Cl. 20; compare
Plin. Nat. 36.124.) For more than a mile
the tunnel is carried under a mountain, of which the highest part is 1000
feet above the level of the lake, and through a stratum of rocky formation
(carnelian), so hard that every inch required to be worked by the chisel.
The remaining portion runs through a softer soil, not much below the level
of the
[p. 1.730]earth, and is vaulted with brick.
Perpendicular shafts (
putei) are sunk at
various distances into the tunnel; and a number of lateral openings or adits
(
cuniculi), some of which separate
themselves into two branches, one above the other, are likewise directed
into it, the lowest at an elevation of five feet from the bottom. Through
these the materials excavated were carried out. The immediate mouth of the
tunnel was at some distance from the margin of the lake, which space was
occupied by two ample reservoirs, intended to break the rush of water before
it entered the emissary, connected by a narrow passage, in which were placed
the sluices. The upper end of the tunnel itself consists of a splendid
archway of the Doric order, nineteen feet high and nine wide, formed out of
large blocks of stone, resembling in construction the works of the Claudian
aqueduct. The mouth through which the waters discharged themselves into the
Liris was more simple, and is represented in the preceding woodcut. The
river lies in a ravine between the arch and foreground, at a depth of 60
feet below, and consequently cannot be seen in the cut. The small aperture
above the embouchure is one of the
cuniculi
above mentioned. It appears that the actual drainage was relinquished soon
after the death of Claudius, either from the perversity of Nero, as the
words of Pliny (
l.c.) seem to imply, or by neglect;
for it was re-opened by Hadrian. (Spart.
Hadr. 22.) For
further information see Hirt, who gives a series of plans and sections of
the works connected with the Lacus Fucinus (
Gebäude d.
Griech. u. Röm. pp. 371-375, pl. xxxi. figs. 14-21).
The modern work of Prince Torlonia (1862-75) is an extension and enlargement
of the tunnel of Claudius.
[
A.R] [
W.W]
