Metamorphoses Book 6: Tereus, Procne, and Philomela
When leaders from neighboring cities were visiting Thebes to offer their condolences, Athens was not among them. Athens was in a war, and Tereus and his army saved Athens from their foe. Procne, the king's daughter, married Tereus as part of Athens' gratitude for Tereus' help. He took her back to Thrace, his home, and after a while there in happiness, she missed her sister. Tereus went back to Athens to bring Philomela back for a visit. Their father, Pandion, was reluctant to let his only other daughter leave, but he did. What Pandion didn't know was that Tereus had fallen in desperate love with Philomela. When they arrived in Thrace, he took Philomela to a hidden cottage in the woods and raped her. She humiliated and furious at the betrayal of her brother-in-law, and she said: "'You'll pay my score one day. I'll shed my shame / And shout what you have done. If I've the chance, / I'll walk among the crowds: or, if I'm held / Locked in the woods, my voice shall fill the woods / And move the rocks to pity.'" Book 6 -- Tereus, Procne, and Philomela, line 46-50. So Tereus cut out her tongue and locked her away where none would ever find her.
Tereus went to his wife and told her that he'd found out that Philomela was dead when he got to Athens. A year passed and Procne mourned her sister. Meanwhile, Philomela wove the story of her kidnapping, rape, and assault into a tapestry and got it to her sister. Procne saw the tapestry and understood what had happened, so during the Bacchic rituals when women go into the woods to worship Bacchus, she rescued Philomela and took her back to the home that she shared with Tereus. The sisters then killed Itys, Procne and Tereus' son, and cooked him. Procne called her husband in and served him the meal. When he called for his son, Philomela came out of the kitchen and presented him with the boy's severed head. In his horror and fury, he chased the women with his sword, vowing to kill them for their treachery. Philomela was changed to a nightingale; Procne became a swallow; and Tereus was transformed to a hoopoe.