CALLISTUS, CALIXTUS I. ST. Pope and whose feast is kept by the Western church, on Oct. 14. His pontificate lasted from 217 to 222. He was much vilified by certain heretical groups which he strongly opposed; their testimony about him in "Philosophumena" is quite unreliable. He mitigated in some respects the penitential discipline of his time, and after him is named the cemetery of San Callisto in Rome, of which at one time he had charge. His relics repose in the church of Santa Maria in Trastevere.