I'm just wondering, in which Greek stories is Achilles' skin said to be impervious (except for his heal)?
I read that earlier stories about the Trojan war had Achilles being stabbed in the back by Paris, rather than shot in the heel. Obviously he couldn't have been invulnerable then.
What's more, the idea of Achilles being unkillable robs him of his humanity (I think) and makes him a very unsympathetic figure.
Any thoughts (or references)?