Emissarium
（
ὑπόνομος). The name given to an artificial channel by
which an outlet is formed to carry off any stagnant body of water (
Ad Fam. xvi.
18). 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 Cephissus through Lake Copais to the sea supplemented by two artificial
emissaria or tunnels. The longer of the two, connecting the lake with the lower course of the
Cephissus, is nearly four miles in length, according to Forchhammer, 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 Copa ïs 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 Cephissus, 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 (
Strab.
ix. p. 407), and it was announced in 1888 that the reclamation of Lake Copaïs
was again to be 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 Heraeum or temple of Heré (iii. 60). These works
unquestionably date from the tyranny of Polycrates, the most flourishing period of Samos,
which ended about B.C. 522.
In Italy the Etruscans were the first great masters in the art of tunnelling, and the Romans
learned it from them. The Cloaca Maxima itself is quite as much an emissary as a sewer,
draining the Forum and the Velabrum, which previously were swamps. (See
Cloaca.) But the greatest Roman emissarium is that of Lake Fucinus.
Iulius Caesar is said to have first conceived the idea of this stupendous undertaking
(
Iul. 44), which was carried into effect by the emperor Claudius (
Tac. Ann. xii. 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 (
Claud. 20). 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 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 earth, and is vaulted with brick. Perpendicular shafts (
putei) are sunk at various distances into the tunnel, and a number of lateral openings
(
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.
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Emissarium.
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The immediate mouth of the tunnel was at some distance from the margin of the lake.
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 illustration.
The modern work of Prince Torlonia
(1862-75) is an extension and enlargement of
the tunnel of Claudius.
