Regardless of the veracity of many of the details in Hippolytus' narration of the life of Callistus, Callistus was valuable to Bp. Zephyrius as he guided the bishop through the formative theology of the day to what he saw as orthodox, as Zephyrius floundered through the many heretical beliefs that sprang up during that era.
The lives of Callistus and both his adversaries, Tertullian and Hippolytus, is shrouded in controversy as some of the policies of each have been termed [[heresy|heretical]]. Hippolytus and Tertullian were especially upset by Callistus' admitting to communion those who had done public penance for murder, adultery, and fornication, as well as by his alleged belief in [[Sabellianism]], a charge from which he attempted to distance himself. Hippolytus was a follower of the Novation [[schism]], from which he later reconciled with the Church, and was elected as an anti-pope by his supporters, while Tertullian became a supporter of [[Montanism]].
He is believed to have died about the year 223, a time not noted for any persecutions. That he was a martyr, perhaps through a popular uprising, is legendary. He was buried in the cemetery of Calepodius on the Aurelian Way. The anniversary of his death is given by the "Depositio Martirum" (''Callisti in viâ Aureliâ miliario III'') and subsequent martyrologies as October 14, the day on which he is still commemorated. His [[relics]] were translated in the ninth century to Santa Maria in Trastevere.