She assisted Troy in the Trojan War, during which she was killed by Achilles or Neoptolemus.

Penthesileia, the daughter of Otrere (Otrera) and Ares, who had accidentally killed Hippolyte and been purified by Priamos, slew many in battle, including Makhaon (Machaon); but later she was herself killed by Akhilleus, who fell in love with the Amazon after she died, and slew Thersites for rebuking him.

When Achilles slew Penthesilea he is said to have also killed Thersites because he treated her body with contempt, and reproached Achilles for his love towards her. 4 Diomedes, a relative of Thersites, is said then to have thrown the body of Penthesilea into the river Scamander, whereas, according to others, Achilles himself buried it on the banks of the Xanthus. 5 Some, further, state that she was not killed by Achilles, but by his son Pyrrhus, 6 or that she first slew Achilles, and Zeus on the request of Thetis having recalled Achilles to life, she was then killed by him. 7

After Hector, the leader of the Trojan army, was killed in the final year of the war, Penthesilea arrived with a small but highly skilled troop of Amazon warriors to help the doomed city against the Greeks. Penthesilea slew many Greeks before being killed in turn by Achilles, the greatest of the Greek warriors at Troy.