The ninth and last circle is ringed by classical and Biblical giants, who perhaps symbolize pride and other spiritual flaws lying behind acts of treachery. The giants are standing on a ledge above the ninth circle of Hell, so that from the Malebolge they are visible from the waist up. They include Nimrod, Ephialtes (who with his brother Otus tried to storm Olympus during the Gigantomachy), Briareus, Tityos, and Typhon. The giant Antaeus (being the only giant unbound with chains) lowers Dante and Virgil into the pit that forms the ninth circle of Hell (Canto XXXI). The traitors are distinguished from the "merely" fraudulent in that their acts involve betraying a special relationship of some kind. There are four concentric zones (or "rounds") of traitors. These rounds correspond, in order of seriousness, to betrayal of family ties, betrayal of community ties, betrayal of guests, and betrayal of liege lords. In contrast to the popular image of Hell as fiery, the traitors are frozen in a lake of ice known as Cocytus, with each group encased in ice to progressively greater depths. Round 1 is named Caïna, after Cain, who killed his brother. Traitors to kindred are here immersed in the ice up to their faces – "the place / where shame can show itself" Mordred, who attacked his uncle/father King Arthur, is one of the traitors here: "him who, at one blow, had chest and shadow / shattered by Arthur's hand" (Canto XXXII). Round 2 is named Antenora, after Antenor of Troy, who according to medieval tradition, betrayed his city to the Greeks. Traitors to political entities, such as parties, cities, or countries, are located here. Count Ugolino pauses from gnawing on the head of his former partner-in-crime Archbishop Ruggieri degli Ubaldini to describe how Ruggieri turned against him after an accidental death of Ruggieri's illegitimate son during a riot and had him imprisoned along with his sons and grandsons, condemning them to death by starvation. A number of correspondences, such as allusions to the same passage of the Aeneid, link this passage to the story of Paolo and Francesca in the second circle, indicating that this icy hell of betrayal is the final result of consent to sin (Cantos XXXII and XXXIII). Round 3 is named Ptolomaea, probably after Ptolemy, son of Abubus, who invited Simon Maccabaeus and his sons to a banquet and then killed them. Traitors to their guests are punished here, lying supine in the ice, which covers them, except for their faces. They are punished more severely than the previous traitors, since the relationship to guests is an entirely voluntary one. Fra Alberigo, who had armed soldiers kill his brother at a banquet, explains that sometimes a soul falls here before Atropos cuts the thread of life. Their bodies on Earth are immediately possessed by a demon, so what seems to be a walking man has reached the stage of being incapable of repentance (Canto XXXIII). Round 4 is named Judecca, after Judas Iscariot, Biblical betrayer of Christ. Here are the traitors to their lords and benefactors. All of the sinners punished within are completely encapsulated in ice, distorted in all conceivable positions. With no one to talk to here, Dante and Virgil quickly move on to the centre of Hell (Canto XXXIV). In the very centre of Hell, condemned for committing the ultimate sin (personal treachery against God), is Satan. Satan is described as a giant, terrifying beast with three faces, one red, one black, and one a pale yellow: he had three faces: one in front bloodred; and then another two that, just above the midpoint of each shoulder, joined the first; and at the crown, all three were reattached; the right looked somewhat yellow, somewhat white; the left in its appearance was like those who come from where the Nile, descending, flows. Satan is waist deep in ice, weeping tears from his six eyes, and beating his six wings as if trying to escape, although the icy wind that emanates only further ensures his imprisonment (as well as that of the others in the ring). Each face has a mouth that chews on a prominent traitor. Brutus and Cassius are feet-first in the left and right mouths respectively, for their involvement in the assassination of Julius Caesar – an act which, to Dante, represented the destruction of a unified Italy and the killing of the man who was divinely appointed to govern the world. In the central, most vicious mouth is Judas Iscariot, the namesake of Round 4 and the betrayer of Jesus. Judas is receiving the most horrifying torture of the three traitors: his head gnawed by Satan's mouth, and his back being forever skinned by Satan's claws. What is seen here is an inverted trinity: Satan is impotent, ignorant, and full of hate, in contrast to the all-powerful, all-knowing, and loving nature of God. The two poets escape Hell by climbing down Satan's ragged fur. They pass through the centre of the earth (with a consequent change in the direction of gravity, causing Dante to at first think they are returning to Hell). The pair emerge in the other hemisphere (described in the Purgatorio) just before dawn on Easter Sunday, beneath a sky studded with stars (Canto XXXIV).
Taken from Dante's Inferno on Wikipedia