[511] _By stairs like this_: The descent from one circle to another grows more difficult the further down they come. They appear to have found no special obstacle in the nature of the ground till they reached the bank sloping down to the Fifth Circle, the pathway down which is described as terrible (_Inf._ vii. 105). The descent into the Seventh Circle is made practicable, and nothing more (_Inf._ xii. I). [512] _Heaven was fired_: As still appears in the Milky Way. In the _Convito_, ii. 15, Dante discusses the various explanations of what causes the brightness of that part of the heavens. [513] _A terrific roar_: Of the water falling to the ground. On beginning the descent they had left the waterfall on the left hand, but Geryon, after fetching one or more great circles, passes in front of it, and then they have it on the right. There is no further mention of the waters of Phlegethon till they are found frozen in Cocytus (_Inf._ xxxii. 23). Philalethes suggests that they flow under the Eighth Circle. [514] _Lure_: An imitation bird used in training falcons. Dante describes the sulky, slow descent of a falcon which has either lost sight of its prey, or has failed to discover where the falconer has thrown the lure. Geryon has descended thus deliberately owing to the command of Virgil. CANTO XVIII. Of iron colour, and composed of stone, A place called Malebolge[515] is in Hell, Girt by a cliff of substance like its own. In that malignant region yawns a well[516] Right in the centre, ample and profound; Of which I duly will the structure tell. The zone[517] that lies between them, then, is round-- Between the well and precipice hard and high; Into ten vales divided is the ground. As is the figure offered to the eye, 10 Where numerous moats a castle's towers enclose That they the walls may better fortify; A like appearance was made here by those. And as, again, from threshold of such place Many a drawbridge to the outworks goes; So ridges from the precipice's base Cutting athwart the moats and barriers run, Till at the well join the extremities.[518] From Geryon's back when we were shaken down 'Twas here we stood, until the Poet's feet 20 Moved to the left, and I, behind, came on. New torments on the right mine eyes did meet With new tormentors, novel woe on woe; With which the nearer Bolgia was replete. Sinners, all naked, in the gulf below, This side the middle met us; while they strode On that side with us, but more swift did go.[519] Even so the Romans, that the mighty crowd Across the bridge, the year of Jubilee, Might pass with ease, ordained a rule of road[520]-- 30 Facing the Castle, on that side should be The multitude which to St. Peter's hied; So to the Mount on this was passage free. On the grim rocky ground, on either side,