"Upon this side he fell down out of heaven And all the land, that whilom here emerged For fear of him made of the sea a veil And came to our hemisphere; and peradventure To flee from him, what on this side Left the place vacant here and back recoiled." (Inf., XXXIV, 121.) The material structure of the Inferno is a series of nine concentric circles--darkness brooding over the whole region,--with ledges, chasms, pits, swamps and rivers. The rivers, though different in name and aspect, appear to be one and the same stream winding its way through the various circles. We see it first as the boundary of Hell proper and it is known as the Acheron. It comes again to view in the fourth circle and is called the Styx. In the seventh circle, second round, it emerges as the red blood stream of Phlegethon. In the very depths of Hell it forms the frozen lake of Cocytus. The circles of Hell, distant from one another, decrease in circumference as descent is made--the top circle being the widest. Galileo estimates that Dante's Hell is about 4,000 miles in depth and as many in breadth at its widest diameter. Its opening is near the forest at the Fauces Averni, near Cuma, Italy, where Virgil places the site of the entrance of his Inferno. Dante's Hell in its moral aspect is Aristotelian. Sins are divided into three great classes, incontinence, bestiality and malice. Incontinence is punished in the five upper circles; bestiality and malice in the City of Dis, lower Hell. More particularly stated, Dante's scheme of punishment in the underworld, not considering the vestibule of Hell, where neutrals are confined, is as follows: 1, Limbo; 2, The Circle of Lust; 3, Gluttony; 4, Avarice and Prodigality; 5, Anger, Rage and Fury; 6, Unbelief and Heresy; 7, Violence; 8, Fraud; 9, Treason. In regard to this plan of punishment three things are to be noted: (a) Though generally following the teaching of St. Thomas Aquinas, here Dante, in his conception of Limbo, differs from his master. Our poet's Limbo, wherein are the souls of unbaptized children and others who died stained with original sin, but without personal grievous guilt, is a much more severe abode than that of the Angelic Doctor. The latter teaches that Limbo is a place or a state, not merely of exemption from suffering and sorrow, but of perfect natural happiness unbroken even by a knowledge of a higher, a supernatural destiny that has never been given. Dante's Limbo, on the other hand, represents the souls in sadness brought about by their constant desire and hope never realizable, of seeing God. They suffer no pain of sense, but they are baffled in their endless yearning for the Beatific Vision. To quote Dante: