In the swamp-like water of the river Styx, the wrathful fight each other on the surface, and the sullen lie gurgling beneath the water, withdrawn "into a black sulkiness which can find no joy in God or man or the universe." Phlegyas reluctantly transports Dante and Virgil across the Styx in his skiff. On the way they are accosted by Filippo Argenti, a Black Guelph from a prominent family. When Dante was forced to leave Florence, Argenti took all his property. When Dante responds "In weeping and in grieving, accursed spirit, may you long remain," Virgil blesses him. Literally, this reflects the fact that souls in Hell are eternally fixed in the state they have chosen, but allegorically, it reflects Dante's beginning awareness of his own sin (Cantos VII and VIII).
      The lower parts of Hell are contained within the walls of the city of Dis, which is itself surrounded by the Stygian marsh. Punished within Dis are active (rather than passive) sins. The walls of Dis are guarded by fallen angels. Virgil is unable to convince them to let Dante and him enter, and Dante is threatened by the Furies (consisting of Alecto, Megaera, and Tisiphone) and Medusa. An angel sent from Heaven secures entry for the poets, opening the gate by touching it with a wand, and rebukes those who opposed Dante. Allegorically, this reveals the fact that the poem is beginning to deal with sins that philosophy and humanism cannot fully understand. Virgil also mentions to Dante how Erichtho sent him down to the lowest circle of Hell to bring back a spirit from there. (Cantos VIII and IX).

Taken from Dante's Inferno on Wikipedia