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 (see Achilles' heel, Achilles' tendon). 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.