430 DRAINING OF LAKE CELANO. 
tunnel, upon a scale of grandeur which does infinite honor to 
the liberality and public spirit of the projectors, and with an 
ingenuity of design and a constructive skill which reflect the 
highest credit upon the professional ability of the engineers 
who have planned the works and directed their execution. The 
length of the Roman tunnel was 18,634 feet, or rather more 
than three miles anda half, but as the new emissary is designed 
to drain the lake to the bottom, it must be continued to the 
lowest part of the basin. It will consequently have a length of 
not less than 21,000 feet, and, of course, is among the longest 
subterranean galleries in Europe. Many curious particulars in 
the design and execution of the original work have been ob- 
served in the course of the restoration, but these cannot here be 
noticed. The difference between the lowest and highest known 
levels of the surface of the lake is rather more than forty feet, 
and the difference between the areas covered by water at these 
levels is not less than nine thousand acres. The complete 
drainage of the lake, including the ground occasionally flooded, 
will recover, for agricultural occupation, and permanently 
secure from inundation, about forty-two thousand acres of as 
fertile soil as any in Italy.* The ground already dry enough 
for cultivation furnishes occupation and a livelihood for a 
population of 16,000 persons,.and it is thought that this num- 
some weieht as evidence that the emissary was not actually open in ancient 
times ; for if the waters had been really connected, the fish of the lake would 
naturally have followed the descending current and established themselves in 
the river as they have done now. 
* Springs rising in the bottom of the lake have materially impeded the pro- 
cess of drainage, and some engineers believe that they will render the complete 
discharge of the waters impossible. It appears that the earthy and rocky 
strata underlying the lake are extremely porous, and that the ground already 
laid dry on the surface absorbs an abnormally large proportion of the precipi- 
tation upon it. These strata, therefore, constitute a reservoir which contri- 
butes to maintain the springs fed chiefly, no doubt, by underground channels 
from the neighboring mountains. But it is highly probable that, after a cer- 
tain time, the process of natural desiccation noticed in note to p. 20, ante, will 
drain this reservoir, and the entire removal of the surface-water will then 
become practicable. 
