Calixtus I, Saint definition of Calixtus I, Saint in the Free Online Encyclopedia.

Calixtus I, Callixtus I, or Callistus I, Saint (kəlĭk`stəs, kəlĭs`təs), c.160–c.222, pope (217–222), a Roman; successor of St. Zephyrinus. As archdeacon to Zephyrinus he established the famous Calixtus Cemetery, where all the popes of the 3d cent. except Calixtus himself are buried. His election to the papacy was opposed by Hippolytus Hippolytus, Saint (hĭpŏl`ĭtəs) [Gr.,=loosed horse], d. c.236, first antipope (c.217–235), theologian, and martyr.
..... Click the link for more information. (later antipope), who accused him of monarchianism and of laxness in disciplining repentant sinners. Calixtus in fact excommunicated the chief monarchianist, Sabellius Sabellianism later was used to include all sorts of speculative ideas that had become attached to the original ideas of Sabellius and his followers. In the East, all monarchians came to be labeled Sabellians.
..... Click the link for more information. . His other important action, to grant absolution under conditions of true contrition to certain classes of sinners (apostates, murderers, adulterers), considered by many as unforgivable, was important in the development of the church's doctrine of penance. Calixtus died in the reign of Alexander Severus and may have been a martyr. He was succeeded by St. Urban I. Feast: Oct. 14.