Callistus was born to a Christian slave who had a Christian master in second-century Rome. He was placed in charge of a Christian bank which went broke. He fled the city, but was caught and sentenced to the treadmill, then later to the tin mines. He was later ransomed and returned to Rome. As a deacon he was hired by Pope Zephyrinus to administer the Church’s property and organize the burial of martyrs in the catacombs on the Appian Way, still named the Cemetery of Saint Callistus.
Eighteen years later in 217 he succeeded Zephyrinus as pontiff, the sixteenth pope. As pope he regulated the discipline of the sacrament of penance, ruling that penitent sinners were welcome in church. He defended the faith against the Adoptionist and Modalist heresies regarding the Holy Trinity and the Person of Jesus Christ. Under the reign of Alexander Severus, he was thrown into prison, and then was tortured by starvation in prison and scourged daily. Finally Callistus was thrown from a window of the house headlong into a well, where he drowned. Callistus died a martyr in 223.