Dante asks about Phlegethon and of Lethe, a river that Virgil forgot to mention. Virgil explains that they have already passed the Phlegethon (the river of boiling blood) and that they will see the Lethe in another circle. He explains that the Lethe is the river where remorseful spirits wash away their guilt, the River of Forgetfulness. Virgil tells Dante to follow him closely along the edge of the stream, so that they can safely cross the burning plain.
Walking between two rounds, they reach a small stream that is so red that it disgusts Dante. Virgil tells Dante this is the most remarkable thing they have yet seen, and Dante asks for an explanation. Virgil gives a long and complicated explanation about the formation of these rivers and how they flow through Hell.
The poets then leave the plains, and Dante is warned to follow the edge of the stream closely to avoid the fire of the burning desert.
