Limbo was a place for writers and poets who died without knowing Christ. Since they didn't know of Christ there was no redemption and in turn they had no knowledge of heaven. Here Dante saw many poets and writers like Socrates and Plato and Democritus. Continuing on they reach the boarder of The Second Circle.
The Second Circle of Hell is a place for those who had the sin of lust. At the border lurked a monster by the name of Minos. Minos was the king of Crete in Greek mythology. He is the prosecutor of all the souls. Minos's job is to decide where each soul should go for their punishment. After a sinner confess's Minos wraps his tail around his body a certain number of times to represent the Circle of Hell the sinner is condemned. Here Dante meets a woman by the name of Francesca, who explains that she was married and had an affair with her husbands brother Paolo da Rimini, in turn both wound up in The Second Circle of Hell. Both are condemned to a spinning torment.
On his way, Dante reaches the Third Circle of Hell, only to see that these souls must lie in the mud. Torrential rains of filth and excrement are showering down upon these sinners. These people are in this circle for being gluttonous. The two keep going and eventually leave the circle for another.
The Fourth Circle, is a place for the Avaricious and Prodigal, here the tormented must sprint toward each other with giant boulders, over and over again. Dante and Virgil watch as these souls, like lab rats, charge back and forth with these large boulders running into each other with no stop for rest. Onward they move.
The Fifth Circle contained the river Styx. This river was for the wrathful, a swamp like nasty cesspool where they have to climb all over each other and struggle to stay on top everyday forever. The Sullen lie at the bottom of this pool of grotesque matter, chocking on the mud, with no hopes of ever seeing the surface.