At the entrance to the fourth circle of hell, Dante and Virgil encounter Pluto (the underworld deity associated with wealth in Roman mythology), who is hailing Satan. Virgil assures Dante that Pluto will not halt their journey, and he shouts at Pluto, telling him that it is willed by God for Virgil and Dante to pass this way. Pluto suddenly falls to the ground like a billowing sail when its mast snaps in a fierce wind.
Pluto is yet another character borrowed from pagan mythology. But whereas in Roman myth he is the king of the underworld, in Dante's hell he merely guards the fourth circle. Virgil disposes of Pluto easily with his powerful words.
Dante wonders if he can do descriptive justice to what he beheld in this area of hell. He compares the souls ceaselessly rushing into each other to waves crashing against each other. Dante asks Virgil who these souls are. Noticing that many of them have bald heads, he asks if they were priests.
Dante again shows some (false?) modesty with regard to how well he can represent his experience in verse. It is at least somewhat ironic that this self-doubt is directly followed by a masterful epic simile of the battling souls to waves crashing together.
Virgil says that half of the souls were spendthrifts on earth, while the other half—with bald heads—were covetous popes and cardinals who hoarded money. Dante wonders if he knows any of these souls, but Virgil says that their suffering has rendered them indistinguishable as individuals. He explains that these souls either squandered or hoarded away what wealth they obtained through Fortune.
In addition to their punishment in hell, the sinners here suffer from being unrecognizable as individuals. They thus have no hope of their names living on in fame (through Dante's poem or otherwise) on earth.
Dante asks Virgil to tell him more about the nature of Fortune. According to Virgil, God established Fortune as a way of dividing up the world's riches among various nations and races. Fortune cannot be understood through science or logic, and men often foolishly blame Fortune for their misfortunes, but Fortune does not hear their curses. Virgil tells Dante that they should continue on their journey.
The personification of Fortune is a pagan idea (prominent in ancient Greek and Roman culture, for example), but Dante has Virgil modify Fortune to fit into a Christian framework. Still, the personified deity adds an oddly polytheistic aspect to Dante's Christianization of classical culture.
Dante and Virgil walk along a dark, bubbling body of water and the marsh which forms at the end of the river Styx. Dante spies naked, savage-looking souls covered in mud and mire in the dark marsh, fighting each other madly. Virgil identifies these souls as the wrathful. He says that the waters of the marsh constantly bubble because there are souls submerged below who constantly sigh in pain and their breath bubbles to the surface. These submerged souls took no joy in life; they were sullen on earth and now they lie sullen in the mud. Virgil leads Dante around the edge of the marshy waters, until they arrive at a large tower.
The wrathful and the sullen are two more examples of fitting punishments in hell. The wrathful are forced to fight forever, the sullen to wallow in the mud. By punishing sinners in this appropriate way, God's justice perfects the sinner's actions, as if their sins need their corresponding punishments to be completed.