text: 760) Zeus' sister and wife Hera alludes to Thetis' chaste resistance to the advances of Zeus, pointing out that Thetis was so loyal to Hera's marriage bond that she coolly rejected the father of gods.Thetis, although a daughter of the sea-god Nereus, was also brought up by Hera, further explaining her resistance to the advances of Zeus.Zeus was furious and decreed that she would never marry an immortal.According to the Achilleid, written by Statius in the 1st century AD, and to non-surviving previous sources, when Achilles was born Thetis tried to make him immortal by dipping him in the river Styx; however, he was left vulnerable at the part of the body by which she held him: his left heel .It is not clear if this version of events was known earlier.In another version of this story, Thetis anointed the boy in ambrosia and put him on top of a fire in order to burn away the mortal parts of his body.She was interrupted by Peleus and abandoned both father and son in a rage.None of the sources before Statius make any reference to this general invulnerability.To the contrary, in the Iliad, Homer mentions Achilles being wounded: in Book 21 the Paeonian hero Asteropaios, son of Pelagon, challenged Achilles by the river Scamander.He was ambidextrous, and cast a spear from each hand; one grazed Achilles' elbow, "drawing a spurt of blood".In the few fragmentary poems of the Epic Cycle which describe the hero's death (i.e.the Cypria, the Little Iliad by Lesches of Pyrrha, the Aethiopis and Iliupersis by Arctinus of Miletus), there is no trace of any reference to his general invulnerability or his famous weakness at the heel.In the later vase paintings presenting the death of Achilles, the arrow (or in many cases, arrows) hit his torso.Peleus entrusted Achilles to Chiron, who lived on Mount Pelion and was known as the most righteous of the Centaurs, to be reared.