Inferno Canto XXIV (the Eighth Circle, Seventh Pouch: the Thieves)
Dante opens this canto with an elaborate extended simile: in the winter, a farmer looks out in dismay at the snow-covered ground (because he can’t get anything done in such weather) but later his worry lightens because he sees the snow has melted. So he goes out to herd his sheep. This is compared to Virgil’s initially-worried-but-later-happier reaction when they reach the collapsed bridge.
He pushes Dante to get a move on and helps him down the rocky bank.
Dante is grateful he doesn’t have one of those leaded cloaks on because the path is really steep. He tells us, if it wasn’t for Virgil’s support, he would’ve given up.
At one point, Dante stops, exhausted. Virgil calls him out for being lazy because, he claims, those who are lazy never earn fame in the world and thus are lost to memory when they die.
Inspired, Dante gets up and announces to Virgil, "I’m buff enough." Or something similar. And so they climb up the far side of the bridge.
Dante keeps talking so that he doesn’t sound weak, and to his surprise, an unknown voice from the next pouch answers him.
They’re at the summit of the bridge at this point so Dante tries to catch a look at the speaker, but it’s too dark to see anything. Dante says they’ll cross the bridge and then find him.
So they do and the first thing Dante sees is that the valley is filled with swarms of coiling snakes.
It’s so horrifying that it exceeds, according to Dante, all the pestilences of Libya or Ethiopia.
And amongst these serpents run a bunch of sinners, with no hope of cover.
The snakes do cruel, nasty things, like binding the sinners' hands with their bodies and knotting themselves around their thighs.
As soon as they’ve been bitten by these serpents, the sinners turn into piles of ash that collect on the ground. But only momentarily. In the next moment, they rise to re-form again, like the mythical phoenix.
The poor sinner-turned-ash-turned-sinner again looks about in bewilderment.
Virgil asks the sinner who he is.
Oddly, the sinner calls himself a mule before actually naming himself as Vanni Fucci and saying he is from Pistoia.
Dante interjects here and tells Virgil to ask him what his sin was. He hints that he knew Vanni Fucci as a "man of blood and anger," meaning that he should be the Fifth Circle.
Vanni overhears Dante and is ashamed of himself. He’s more ashamed at having been caught by Dante than by his actual sin, which was stealing holy relics from a church. He’s a thief.
Then, he tells Dante not to take too much joy at seeing him suffer, because Dante’s beloved Whites are going to fall.
Vanni launches into a cryptic prophecy, which translates as: Pistoia will first throw out the Blacks, but they will strike back with a military force (or poetically a "vapor" from Mars, the god of war) from Val di Magra and deliver the Whites a smashing defeat.