Posilipo
a mountain of Italy, on the N. W. of Naples, close by the city, from of old a noble site for the villas of wealthy citizens. It is remarkable for the tunnel known as the Grotto of Posilipo, through which the road from Naples to Pozzuoli passes. The grotto varies in height from 20 feet to 80 or more, is 20 to 30 feet wide, and 755 yards long. It is traditionally said to have been made in the reign of Augustus, but is probably earlier. Above the eastern archway of the grotto is the so-called "Tomb of Vergil." At the base of the hill anciently stood the poet's villa. During the Middle Ages the common people believed the grotto to be the work of the poet, whom they regarded as a great magician. Two other tunnels penetrate through the hill, one to the N. of the grotto, 800 yards long, 39 feet high, and 33 feet broad, made for the tramway, and another constructed at the command of Agrippa in 37 B. C., but only discovered in 1812.