According to later legends, Achilles was invulnerable on all of his body except for his heel, which was his only weakness. When Achilles was born, his mother Thetis tried to make him immortal by dipping him in the river Styx, but she forgot to wet the heel she held him by, leaving him vulnerable at that spot. In the Iliad, Homer mentions Achilles being wounded, which contradicts the later legends of his invulnerability. In Book 21, the Paeonian hero Asteropaeus challenged Achilles by the river Scamander and cast two spears at once, one of which grazed Achilles elbow and drew blood. Therefore, the weakness of the Greek hero Achilles was his heel.