Polyxena was the youngest daughter of King Priam and Queen Hecuba of Troy. Here you see her drawing water at the well - while Achilles is watching her! You can see Achilles on the other side of the vase:
Achilles had felt a strong sympathy towards this Trojan princess, and he told her of his only vulnerability: his heel. With that knowledge, Prince Paris, Polyxena's brother, was able to ambush Achilles and kill him. You can read about Polyxena's sad fate here: The Sacrifice of Polyxena.