The New Advent Catholic Encyclopedia

 Although the martyrdom of St. Agatha is authenticated, and her veneration as a saint had even in antiquity spread beyond her native place, we still possess no reliable information concerning the details of her glorious death. ………….. According to them [the Acts]  Agatha, daughter of a distinguished family and remarkable for her beauty of person, was persecuted by the Senator Quintianus with avowals of love. As his proposals were resolutely spurned by the pious Christian virgin, he committed her to the charge of an evil woman, whose seductive arts, however, were baffled by Agatha's unswerving firmness in the Christian faith. Quintianus then had her subjected to various cruel tortures. Especially inhuman seemed his order to have her breasts cut off, a detail which furnished to the Christian medieval iconography the peculiar characteristic of Agatha. But the holy virgin was consoled by a vision of St. Peter, who miraculously healed her. Eventually she succumbed to the repeated cruelties practised on her.