According to the Liber Pontificalis, he was Greek by birth; however this is uncertain and disputed by modern western historians arguing that the authors of Liber Pontificalis confused him with that of the contemporary author Xystus who was Greek student of Pythagoreanism. He restored the relations with the African and Eastern Orthodox churches which had been broken off by his predecessor on the question of heretical baptism.
In the persecutions under Emperor Valerian I in 258, numerous bishops, priests, and deacons were put to death. Pope Sixtus II was one of the first victims of this persecution, being beheaded on August 6. He was martyred along with six deacons—Januarius, Vincentius, Magnus, Stephanus, Felicissimus and Agapitus .
He is thought to be the author of the pseudo-Cyprianic writing Ad Novatianum, though this view has not found general acceptance. Another composition written at Rome, between 253 and 258, is generally agreed to be his.
The following inscription honoring was placed on his tomb by Pope Saint Damasus I:
It is this Sixtus who is referred to by name in the Roman Canon of the Mass.. He and his companion-martyrs are commemorated with an optional memorial on 7 August.
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