St. Agnes was the daughter of wealthy and distinguished parents in Rome during the 4th century. She was a beautiful young woman, but was intent on devoting her entire life to God.
However, that life was cut short when various Romans tried to convince her to go against her personal vow.
A 19th-century Cyclopædia of Female Biography gives a succinct summary of her life from Christian tradition.
She was but thirteen at the time of her glorious death. Her riches and beauty excited many of the young noblemen of Rome to seek her in marriage, but Agnes answered them all that she had consecrated herself to a heavenly spouse. Her suitors accused her to the governor as a Christian, not doubting that threats and torments would overcome her resolution. The judge at first employed the mildest persuasions and most inviting promises to which Agnes paid no attention.
However, the governors attempts to trip her up did nothing and it started to greatly irritate him. He ordered her execution and she died at the sword for her refusal to give-in to the advances of the suitors.
These stories of her heroic death spread throughout the early Church and gained her a reputation, as the Catholic Encyclopedia explains.
Since the close of the 4th century the Fathers of the Church and Christian poets have sung her praises and extolled her virginity and heroism under torture.
She would later be one of the primary patrons of purity and chastity, invoked by many men and women in their time of temptation.