If a man will take his stand on the lower heights of the hills behind Castellammare, he will find that he looks over Pompeii, over Bosco Reale lying on the first slopes which swell upward from the plain, into the mouth of the gap which parts Vesuvius from Somma. Even from that distance he will obtain a forcible impression of the black cliff of Somma, towering almost sheer to the height of a thousand feet above the bottom of the gap, while the outer face of the same rock wall slopes towards the sunny plain and the woods of Ottajano with an incline so gentle as to be comparatively easy of ascent. Clearly the two faces of Somma have been differently formed. The sheer one was, at least in part, the actual wall of the prehistoric crater, that caldron in which the volcanic forces raged in days so ancient that they had been clean forgotten when the Romans ruled the land. The present cone did not exist. The circuit of Monte Somma was unbroken, and lay clothed with green meadows up to the very summit. But where, then, is the rest of that gigantic wall? It was blown away by the eruption that destroyed Pompeii. This is the first tremendous fact which the visitor to Naples has to realise; and it is well worth while to absorb it thoroughly before setting foot upon the mountain, for nothing else seen there carries with it the same impression of overwhelming, cataclysmal awe. It is from a distance that the terror of the thing can be appreciated best. When one goes forward from the observatory on the mountain-side, skirting the flank of the eruptive cone, into that portion of the gap which is called the Atrio del Cavallo--though it would at certain times be found as safe to stable a steed in the Kelpie's flow as in this wilderness of burnt rock--the sight of the steep wall towering on one's left is infinitely striking. But at so close a distance, and in the immediate neighbourhood of so many other sights, it is scarcely possible to concentrate one's thoughts on the girth of the ancient crater. To comprehend the extent of the wall which has been blown away one must go further off, till one can distinguish the shape of Somma's wall, till one's eye can measure the vast size of the crater which would be formed by its completion, even allowing for the doubts which have been raised whether the circuit could have been so vast as this measurement would imply. There are some shattered fragments of the wall to be seen upon the south or seaward side of the volcano. The ridge where the white observatory building stands is one; another, named the "pedementina," appears as a shoulder of the mountain, clearly distinguishable from Naples. But these scattered remnants help little towards the general impression. It is by contemplating Somma that one learns to comprehend the appalling nature of the convulsion which, with little warning, blasted away so immense a portion of the mountain regarded by those who dwelt beneath it as one of the eternal hills.