The last two circles of Hell punish sins that involve conscious fraud or treachery. These circles can be reached only by descending a vast cliff, which Dante and Virgil do on the back of Geryon, a winged monster traditionally represented as having three heads or three conjoined bodies. However, Dante describes Geryon as having three mixed natures: human, bestial, and reptilian. Dante's Geryon is an image of fraud, having the face of an honest man on the body of a beautifully colored wyvern, with the furry paws of a lion and a poisonous sting in the pointy scorpion-like tail (Canto XVII). The fraudulent – those guilty of deliberate, knowing evil – are located in a circle named Malebolge ("Evil Pockets"). This circle is divided into ten Bolgie, or ditches of stone, with bridges spanning the ditches: Bolgia 1: Panderers and seducers march in separate lines in opposite directions, whipped by demons (here Dante makes reference to a recent traffic rule developed for the Jubilee year of 1300 in Rome: keep to the right). Just as the panderers and seducers used the passions of others to drive them to do their bidding, they are themselves driven by demons to march for all eternity. In the group of panderers, the poets notice Venedico Caccianemico, who sold his own sister to the Marchese d'Este. In the group of seducers, Virgil points out Jason, who gained the help of Medea by seducing and marrying her only to later desert her for Creusa. Jason also seduced Hypsipyle, but "abandoned her, alone and pregnant" (Canto XVIII). Bolgia 2: Flatterers also exploited other people, this time using language. They are steeped in human excrement, which represents the words they produced. Alessio Interminei of Lucca and Thaïs are seen here. (Canto XVIII). Bolgia 3: Dante now forcefully expresses his condemnation of those who committed simony. Those who committed simony are placed head-first in holes in the rock (resembling baptismal fonts), with flames burning on the soles of their feet. One of the simoniacs, Pope Nicholas III, denounces two of his successors, Pope Boniface VIII and Pope Clement V, for the same offence. Simon Magus, who offered gold in exchange for holy power to Saint Peter, is also seen here. The simile of baptismal fonts gives Dante an incidental opportunity to clear his name of an accusation of malicious damage to the font in the church of San Giovanni dei Fiorentini (Canto XIX). Bolgia 4: Sorcerers, astrologers, and false prophets here have their heads twisted around on their bodies backward, so that they "found it necessary to walk backward, / because they could not see ahead of them." While referring primarily to attempts to see into the future by forbidden means, this also symbolises the twisted nature of magic in general. In this Bolgia, Dante sees Amphiaraus, Tiresias (whose double transformation is also referenced), Tiresias' daughter Manto, Aruns, Michael Scot, Alberto de Casalodi, and Guido Bonatti, among others (Canto XX). Bolgia 5: Corrupt politicians (barrators) are immersed in a lake of boiling pitch, which represents the sticky fingers and dark secrets of their corrupt deals. The barrators are the political analogue of the simoniacs, and Dante devotes several cantos to them. They are guarded by devils called the Malebranche ("Evil Claws"), who provide some savage and satirical black comedy – in the last line of Canto XXI, the sign for their march is provided by a fart: "and he had made a trumpet of his ass." The leader of the Malebranche, Malacoda ("Evil Tail"), assigns a troop to escort Virgil and Dante safely to the next bridge. The troop hook and torment one of the sinners (identified by early commentators as Ciampolo), who names some Italian grafters and then tricks the Malebranche in order to escape back into the pitch. The promise of safe conduct the poets received from the demons turns out to have limited value (and there is no "next bridge"), so the poets are forced to scramble down into the sixth Bolgia (Cantos XXI through XXIII). Bolgia 6: In the sixth Bolgia, the poets find the hypocrites listlessly walking along wearing gilded lead cloaks, which represent the falsity behind the surface appearance of their actions – falsity that weighs them down and makes spiritual progress impossible for them. Dante speaks with Catalano and Loderingo, two members of the Jovial Friars, an order that had acquired a reputation for not living up to its vows and was eventually suppressed by Pope Sixtus V. Caiaphas, the high priest responsible for ordering Jesus crucified, is also seen here, crucified to the ground and trampled (Canto XXIII). Bolgia 7: Two cantos are devoted to the thieves. They are guarded by the centaur Cacus, who has a fire-breathing dragon on his shoulders and snakes covering his equine back (in Roman mythology, Cacus was not a centaur but a monstrous fire-breathing giant slain by Heracles). The thieves are pursued and bitten by snakes and lizards. The full horror of the thieves' punishment is revealed gradually: just as they stole other people's substance in life, their very identity becomes subject to theft here, and the snake bites make them undergo various transformations. Vanni Fucci is turned to ashes and resurrected. Agnello is blended with the six-legged reptile that is Cianfa. Buoso exchanges shapes with the four-legged Francesco: "The soul that had become an animal, / now hissing, hurried off along the valley; / the other one, behind him, speaks and spits" (Cantos XXIV and XXV). Bolgia 8: Two further cantos are devoted to fraudulent advisers or evil counsellors, who are concealed within individual flames. These are not people who gave false advice, but people who used their position to advise others to engage in fraud. Ulysses and Diomedes are condemned here for the deception of the Trojan Horse. Ulysses tells the tale of his fatal final voyage (Dante's invention) where he left his home and family to sail to the end of the Earth only to have his ship founder near Mount Purgatory; Ulysses also mentions of his encounter with Circe, stating that she "beguiled him." Guido da Montefeltro recounts how he advised Pope Boniface VIII to capture the fortress of Palestrina, by offering the Colonna family inside it a false amnesty and then razing it to the ground after they surrendered. Guido describes how St. Francis came to take his soul to Heaven because of Guido's subsequent joining of the Franciscan order, only to have a demon assert prior claim. Although Boniface had absolved Guido in advance for his evil advice, Dante points out the invalidity of that, since absolution requires contrition, and a man cannot be contrite for a sin at the same time that he is intending to commit it (Cantos XXVI and XXVII). Bolgia 9: In the ninth Bolgia, a sword-wielding demon hacks at the Sowers of Discord, dividing parts of their bodies as in life they divided others. As they make their rounds the wounds heal, only to have the demon tear apart their bodies again. Dante encounters Muhammad, who tells him to warn the schismatic and heretic Fra Dolcino. Dante describes Muhammad as a schismatic, apparently viewing Islam as an off-shoot from Christianity, and similarly Dante seems to condemn Ali for schism between Sunni and Shiite . In this Bolgia, Dante also encounters Bertran de Born, who carries around his severed head like a lantern (a literal representation of allowing himself to detach his intelligence from himself), as a punishment for (Dante believes) fomenting the rebellion of Henry the Young King against his father Henry II (Cantos XXVIII and XXIX). Bolgia 10: In the final Bolgia, various sorts of falsifiers (alchemists, counterfeiters, perjurers, and impostors) – who are a "disease" on society – are themselves afflicted with different types of diseases. Potiphar's wife is briefly mentioned for her false accusation of Joseph. The Achaean spy Sinon suffers from a burning fever for tricking the Trojans into taking the Trojan Horse into their city; Sinon is here rather than in Bolgia 8 because his advice was false as well as evil. Gianni Schicchi is a 'rabid goblin' for forging the will of Dante's relative Buoso Donati. Myrrha suffers from madness for disguising herself to commit incest with her father King Theias. In Sayers's notes on her translation, she remarks that the descent through Malebolge "began with the sale of the sexual relationship, and went on to the sale of Church and State; now, the very money is itself corrupted, every affirmation has become perjury, and every identity a lie" so that every aspect of social interaction has been progressively destroyed (Cantos XXIX and XXX).
Taken from Dante's Inferno on Wikipedia