Tereus was the son of Ares, the god of war, and became a Thracian king. He married a woman named Procne and they had a son named Itys.
Tereus desired his wife's sister, Philomela. He forced himself upon her, then cut her tongue out and held her captive so she could never tell anyone. He told his wife that her sister had died. Philomela wove letters in a tapestry depicting Tereus' crime and sent it secretly to Procne. In revenge, Procne killed Itys and served his flesh in a meal to his father Tereus. When Tereus learned what she had done, he tried to kill the sisters but all three were changed by the Olympian Gods into birds. Tereus became a hoopoe; Philomela became the nightingale whose song is a song of mourning for the loss of innocence; Procne became the swallow.