Old Rome: A Handbook to the Ruins of the City and the Campagna

by Robert Burn

The Alban lake belongs to the water system of the Tiber, and has most of its outlets on the western side. It has been supposed that a subterranean communication exists between this lake and that of Nemi, but Nibby asserts that this is impossible, as the level of the lake of Nemi is higher than that of the Alban lake. The circumference of this sheet of water is more than six miles, and it is nearly elliptical in shape. The story of the sudden rise of its waters in the sixth year of the siege of Veii is well known, and the response of the Delphic oracle as given in Livy.

Cicero gives a distinct account of the drainage of the lake. “We are told, he says, by the Annalists, that during the siege of Veii, when the Alban lake had risen to an unusual height, a Veientine noble fled to Rome as a deserter, and declared that it was written in the books of fate which were kept at Veii, that Veii could not be taken, so long as the lake was overflowing its banks, and that if the lake were tapped, and flowed into the sea by its own channel and stream, it would be fatal to the Roman nation, but that if the water were so discharged as to make it impossible for it to reach the sea, then the Romans would be victorious. In consequence of this our ancestors contrived that admirable plan for drawing off and dispersing the water of the lake.”

From this passage it would seem likely that the whole object of the drainage of the lake was to obtain a constant supply of water for the irrigation of the Campagna. In another passage Cicero states his opinion still more clearly, that the work was really undertaken for the benefit of suburban agriculture. “The Veientine prophecy that if the water of the Alban lake rose above its margin and flowed into the sea, Rome would perish; but that if it were checked, Veii would be taken, in consequence of which the Alban water was diverted, was intended to benefit the suburban farms, and not to secure the safety of Rome.” What appears strange, is that it should have been necessary to appeal to a superstitious motive in the case of a people evidently so far advanced in civilization as to be capable of carrying out an engineering work of such difficulty in a single year.[139]

Emissarium of the Alban lake.

The tunnel which still carries off the superfluous water of the lake is cut through solid peperino and occasional masses of still harder basaltic lava. It is more than a mile and a half in length, from seven to ten feet in height, and never less than four feet in breadth. The height of the edge of the lake basin above the level of its water at the part which is pierced by the tunnel is 430 feet. Three vertical shafts are still discoverable, by which a draft of air was created and the rubbish was removed, and one slanting shaft for the entrance and exit of the miners. The rock was cut with a chisel an inch wide, as may be seen from the marks left upon the sides of the tunnel.

At the points where the water enters and leaves the tunnel, considerable pains have been taken to regulate the flow. The channel of stonework at the mouth is placed in a slanting direction so as to break the force of the rush of water. At the end of this first channel is a cross wall with openings, protected by gratings to catch the leaves and floating rubbish. Behind this is a reservoir, similar to the cisterns in use in the Roman aqueducts, allowing the mud to settle before the water entered the tunnel. Next to the tunnel itself there is a closed building to protect the canal from the fall of rocks and stones, and the actual entrance into the rock is faced with a massive portal of wedge-shaped blocks of stone. The water in this enclosure is now used by the fishermen of the lake as a receptacle for keeping fish, and is for this purpose provided with sluices. Hirt thinks that these arrangements at the mouth are very ancient.[140] Others ascribe them to the imperial era.

The point where the tunnel emerges from the mountain on the west of Castel Savelli, nearly a mile from Albano, is called Le Mole. The water was there received in a long troughlike reservoir arched over with a stone vaulted roof. From this it ran through five smaller openings into five separate channels, and was so dispersed into the fields for irrigation. At the present time the whole stream is united, and after passing the road to Anzio, thirteen miles from Rome, takes the name of Rio d’Albano, receives the brook from the valley of Apiolæ, and joining the Acqua Acetosa and Cornacciola crosses the Ostian way near Tor di Valle, three miles and a half from Rome, and then discharges itself into the Tiber.

It is the opinion of some archæologists that the Romans brought engineers from Greece to superintend the Alban tunnel. This supposition, however, is not necessary. If the Italian engineers could construct the Cloaca Maxima they would be fully equal to the task of tapping the Alban lake.

The physical conformation of Central Italy compelled its inhabitants to turn their attention at an early period to the construction of drains and other hydraulic works. Considerable artificial channels were rendered necessary in order to regulate the flow of the Arno and Tiber in the neighbourhood of Chiusi. In southern Etruria, the district now known as the pestilent Maremma, could only have been rendered healthy by systematic artificial drainage. The sites of Populonia, Saturnia, Cosa, Veii, and Cære were thus rendered habitable and fertile, and a great part of Latium Maritimum, the Pomptine marshes, and the tract about Suessa Pometia must have been artificially and skilfully drained at the time of the greatest prosperity of those places. Many of the ancient cities of Central Italy had tunnels bored underneath their streets which served as thoroughfares connecting the different parts of the city, or as secret passages leading out into the country. Such tunnels are found at Præneste and Alba Fucensis. An account of the attempted escape of Marius from Præneste, by means of the tunnels, is given by Velleius. The catacombs show that the same genius for tunnelling operations existed at a later time among the Italians of the empire.

Alban Mount.