From the St. Andrew Daily Missal (1962 Edition):-
St. Callistus I (217-222*) was one of the great popes of the Third Century. As a deacon, he was charged with the administration of the Church's property and with gathering together the bodies of the martyrs; he organised the famous cemetery on the Appian Way, called after him San Callisto, which has made his name familiar. As pope, he regulated the discipline of the Sacrament of Penance, and had to face the schism of Hippolytus. He was probably killed in a populr insurrection and has been honoured as martyr since the Seventh Century."
*Presumably the dates of his pontificate.Sancte Calliste, ora pro nobis.