According to the 13th-century Golden Legend (III.15) by Jacobus de Voragine, fifteen-year-old Agatha, from a rich and noble family, made a vow of virginity and rejected the amorous advances of the Roman prefect Quintianus, who thought he could force her to turn away from her vow and marry him. His persistent proposals were consistently spurned by Agatha. This was during the persecutions of Decius, so Quintianus, knowing she was a Christian. reported her to the authorities. Quintianus himself was governor of the district.
He expected her to give in to his demands when she was faced with torture and possible death, but she simply reaffirmed her belief in God by praying: “Jesus Christ, Lord of all, you see my heart, you know my desires. Possess all that I am. I am your sheep: make me worthy to overcome the devil.” With tears falling from her eyes, she prayed for courage. To force her to change her mind, Quintianus sent Agatha to Aphrodisia, the keeper of a brothel, and had her imprisoned there. Agatha never lost her confidence in God.
Quintianus sent for her again, argued, threatened, and finally had her imprisoned and tortured. She was stretched on a rack to be torn with iron hooks, burned with torches, and whipped. Amongst the tortures she underwent was the cutting off of her breasts with pincers. After further dramatic confrontations with Quintianus, represented in a sequence of dialogues in her passio that document her fortitude and steadfast devotion, Agatha was then sentenced to be burnt at the stake, but an earthquake saved her from that fate; instead, she was sent to prison where St. Peter the Apostle appeared to her and healed her wounds.
Agatha died in prison, probably in the year 251 according to the Legenda Aurea. Although the martyrdom of Agatha is authenticated, and her veneration as a saint had spread beyond her native place even in antiquity, there is no reliable information concerning the details of her death.
Osbern Bokenham, A Legend of Holy Women, written in the 1440s, offers some further detail