King Pandion of Athens had two daughters, Procne and Philomela. When Athens was threatened, King Tereus of Thrace came to its aid. Out of gratitude, Pandion offered Tereus either daughter in marriage, and Tereus chose Procne.
They lived in Thrace for years and had a son named Itylus. Procne grew homesick and longed to see her sister Philomela. At her repeated requests, Tereus sailed to Athens to fetch Philomela. On the return voyage, he was inflamed by Philomela's maidenly beauty.
He seized her, cut out her tongue, and imprisoned her in a lonely hut in the woods. He lied to Procne, claiming Philomela was dead. Imprisoned for a year, Philomela wove her painful story into a robe's web and managed to send it to her sister.
Upon receiving the message, Procne rescued Philomela from the woods. Back at the palace, burning for revenge, the two sisters killed Itylus and served him to his father. When Tereus discovered the truth, he chased them into the woods with his sword. There, the gods transformed Procne into a swallow, Philomela into a nightingale, and Tereus into a hoopoe.