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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
Emissarium of lake Fucino.
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]
1 Some of Fabricius' statements have been corrected from notes kindly communicated by Mr. J. Theodore Bent, who visited Samos in 1886.
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