In a small, beautiful valley at the foot of the Eden mountain, Dante sees the very serpent who tempted Eve: a reptile that would be some 5,500 years old, according to Medieval chronology from the beginning of the world to the poet's time. Anyway, time to re-pent!
P.S. Dante shows to follow the same tradition as Milton did, i.e. that the Serpent was a normal snake being haunted by Satan. While, according to other interpretations, the beast was the devil himself.