Dante the narrator begins the canto by making a little speech to Florence, telling her to rejoice, since no less than five of the thieves he has just met are prominent Florentines. But great disaster is coming toward her, and he hopes it will come soon, since it must come, because it will only bring him more pain later.
Dante and Virgil move on, Virgil helping Dante with the hard ascent of the next bridge. Remembering what he saw then (in the Eighth Bolgia), Dante the narrator says he still grieves over it, and feels fresh resolve not to misuse the powers he has been given. What Dante see are tongues of flame, as many as fireflies on a summer night, and Virgil tells him that within each is a tormented spirit, and within one flame whose top is split are two spirits, Ulysses (Odysseus) and Diomedes, who advised the Greeks to deceive the Trojans with the Trojan Horse. At Dante's urgent request, Virgil conjures Ulysses to speak and tell where he went on his last voyage and how he died. Ulysses tells how, hungry always for new experience, he did not go back to his wife and son and kingdom after he left Circe but on to the Pillars of Hercules. There he persuaded his men to sail on into the open Atlantic, telling them "You were not born to live like beasts, but to follow virtue and knowledge" (lines 119-120), and to have as full an experience of the world as possible before your brief life ends. Ulysses goes on to tell how they sailed on their crazy journey for many days, until finally they saw a mountain rising out of the sea. From that mountain a storm rose and sank their ship.
In the Eighth Bolgia are those who used their high gifts of intelligence and eloquence to persuade other to commit fraud, stealing their integrity as here the flame steals the form of the sinner. Ulysses was not nearly as much of a hero in medieval versions of the story of Troy as he was in Homer, whom Dante could not read, knowing no Greek. Nevertheless, many have felt that he is presented as truly heroic here, in a version of his story that is Dante's original creation. Certainly the speech Ulysses makes is one of the best-known passages of the poem. Those who see Ulysses as heroic believe that Dante sympathized with his aspiration for full experience and knowledge, even though, given the theology of Dante's day, Ulysses had to be condemned. Others have argued that, splendid as the rhetoric of the speech may be, Ulysses himself calls his journey crazy, and to make it he has to turn his back on all his human ties.