Note 518 — CANTO XVIII.

The extremities: The Malebolge consists of ten circular pits or fosses, one inside of another. The outermost lies under the precipice which falls sheer from the Seventh Circle; the innermost, and of course the smallest, runs immediately outside of the ‘Well,’ which is the Ninth Circle. The Bolgias or valleys are divided from each other by rocky banks; and, each Bolgia being at a lower level than the one that encloses it, the inside of each bank is necessarily deeper than the outside. Ribs or ridges of rock—like spokes of a wheel to the axle-tree—run from the foot of the precipice to the outer rim of the ‘Well,’ vaulting the moats at right angles with the course of them. Thus each rib takes the form of a ten-arched bridge. By one or other of these Virgil and Dante now travel towards the centre and the base of Inferno; their general course being downward, though varied by the ascent in turn of the hog-backed arches over the moats.