which occupies an extinct crater. The lake is three miles in
circumference, and 300 feet deep, and passes out by an artificial
_emissarium_, made by Trajan. The water is calm and marvellously
clear.
Trajan erected on this lake a floating palace, 500 feet in length, 270
feet in breadth, and 60 feet deep. It was of wood, joined with bronze
nails, and lead plated outside; the inside was lined with marble, and
the ceilings were of bronze. The water for use and ornament was
supplied from the Fount Juturna by means of pipes. Signor Marchi, a
Roman, in 1535 descended in a diving-bell and explored this curious
palace, which had sunk beneath the waters. He left an account of his
discoveries. (See Brotier's "Tacitus," Sup. Ap., and Notes on Trajan.)
A large fragment of the wood-work is preserved in the Kircherian
Museum.
_On the opposite side_ is the small medieval town of