Nothing is more certain than the bet that the Vesuvius upon which the ancient Romans and the Greek settlers of Southern Italy looked, was a mountain differing entirely in its form and appearance from that with which we are familiar. The Vesuvius known to the ancients was a great truncated cone, having a diameter at its base of eight or nine miles, and a height of about 4,000 feet. The summit of this mountain was formed by a circular depressed plain, nearly three miles in diameter, within which the gladiator Spartacus, with his followers, were besieged by a Roman army. There is no evidence that at this time the volcanic character of the mountain was generally recognised, and its slopes are described by the ancient geographers as being clothed with fertile fields and vineyards, while the hollow at the top was a waste overgrown with wild vines. [Illustration: Fig. 14.--Crater of Vesuvius in 1756. (From a drawing made on the spot)] But in the year 79 a terrible and unexpected eruption occurred, by which a vast, crateral hollow was formed in the midst of Vesuvius, and all the southern side of the great rim surrounding this crater was broken down. Under the materials ejected during this eruption, the cities of Pompeii, Herculaneum, and Stabiæ were overwhelmed and buried. Numerous descriptions and drawings enable us to understand how in the midst of the vast crater formed in the year 79 the modern cone has gradually been built up. Fresh eruptions are continually increasing the bulk, or raising the height of the Vesuvian cone. The accompanying drawings made by Sir William Hamilton enable us to understand the nature of the changes which have been continually taking place at the summit of Vesuvius. The drawing fig. 14 shows the appearance presented by the crater in the year 1756. [Illustration: Fig. 15.--The Summit of Vesuvius in 1767. (From an original drawing.)] [Sidenote: VESUVIUS IN MODERN TIMES.] At this time we see that inside the crater a series of cones had been built up one within the other from which lava issued, filling the bottom of the crater and finding its way through a breach in its walls, down the side of the cone. It is evident that the ejected materials falling on the sides of the innermost cone would tend to enlarge the latter till its sides became confluent with the cone surrounding it, and if this action went on long enough, the crater would be entirely filled up and a perfect cone with only a small aperture at the top would be produced. But from time to time, grand and paroxysmal outbursts have occurred at Vesuvius, which have truncated the cone, and sometimes formed great, cup-shaped cavities, reaching almost to its base, like that shown in fig. 13. In 1767 the crater of Vesuvius, as shown in fig. 15, contained a single small cone in a state of constant spasmodic outburst, like that of Stromboli. [Illustration: Fig. 16.--Summit of Vesuvius in 1848.]