In their mining operations and in the formation of some aqueducts, we have seen that the ancients were obliged to tunnel. But their most remarkable works of this kind are the subterranean passages, by which the Romans drained many large lakes. One such channel, through which the lake Fucino discharged its water, is still nearly perfect. It is more than three miles long, one mile of the distance being carried through the hardest rock, under a mountain 1000 feet in height. Perpendicular and lateral shafts were sunk into the tunnel for the convenience of working, and 30,000 men were employed on the spot at the same time. Where the tunnel passes through earth it in vaulted with brick. After the aqueducts the baths follow in a natural order. The great fondness of the Greeks and Romans for ablution, which the warmth of their climate rendered a great luxury, early led to ample provision for bathing, both public and private. Both people were familiar with the use of the hot-air bath, which was especially employed by the Spartans; but the warm-water bath, succeeded often by the cold douche, or plunging bath, was most usual. All the appliances that could minister to comfort and luxury in this department were not only known but common; and to such a degree did the splendor of the public baths at Rome attain, that it was not unusual for emperors themselves to bathe amid a throng of meaner citizens. Lofty, vaulted rooms, lighted by glass, with temperatures artificially contrived to suit the different states of the bather; spacious basins, lined with marble, and fitted with marble, bronze, or even silver benches, were plentifully supplied with water, hot, cold, pure, or scented with the most precious perfumes and essences. Porticoes and vestibules adorned with finished works of art, where the bather took his exercise listening to the recitations of poets, the declamation of orators, or the subtle disputes of philosophy; or perhaps reclined in luxurious ease amid the pleasant murmur of adjacent fountains; cool avenues for the promenaders at mid-day, lawns, terraces, and all the best efforts of their ornamental gardening, were united in the Roman Thermæ, or great public establishments for bathing and recreation, planned and executed in the imperial city and provincial towns. One of these, the Thermæ of Caracalla, was more than a mile in circuit.