A flattened conical mountain, 4161 ft. in height, and an active volcano on the Bay of Naples, 10 m. SE. of the city; it was by eruption of it that the two cities of Herculaneum and Pompeii were overwhelmed in 79 A.D.; its crater is half a mile in diameter, and has a depth of 350 ft.; there are some 60 eruptions on record, the latest being in 1891.