Yes, Achilles is not invulnerable in The Iliad (he gets wounded and 'dark blood' comes out). In later traditions, (what you mentioned and even in the epic 'Fall of Troy') he is invulnerable.
I specifically wanted to find the source of that bit of story our good friend dath kimbula mentioned (Achilles' death linked to a girl he meets during the time period mentioned in 'The Iliad'). She can't be Cressida either.
I've never heard of such a story. His death is sometimes linked to some girl/girls months AFTER that time period (after Memnon is killed, Amazons are killed etc.)
the girl is Polyxena
but that's just a by-story





ow Latin thamayi. eth Achilles ge death eka gena kiyana hinda pennuwe