CALIXTUS II, or Callistus III, (d. 1124), pope from 1119 to 1124, was Guido, a member of a noble Burgundian family, who became archbishop of Vienne about 1088, and belonged to the party which favoured reform in the Church. In September 1112, after Pope Paschal II. had made a surrender to the emperor Henry V., Guido called a council at Vienne, which declared against lay investiture, and excommunicated Henry. In February 1119 he was chosen pope at Cluny in succession to Gelasius II., and in opposition to the anti-pope Gregory VIII., who was in Rome. Soon after his consecration he opened negotiations with the emperor with a view to settling the dispute over investiture. Terms of peace were arranged, but at the last moment difficulties arose and the treaty was abandoned; and in October 1119 both emperor and anti-pope were excommunicated at a synod held at Reims. The journey of Calixtus to Rome early in 1120 was a triumphal march. He was received with great enthusiasm in the city, while Gregory, having fled to Sutri, was delivered into his hands and treated with great ignominy. Through the efforts of some German princes negotiations between pope and emperor were renewed, and the important Concordat of Worms made in September 1122 was the result. This treaty, made possible by concessions on either side, settled the investiture controversy, and was confirmed by the Lateran council of March 1123. During his short reign Calixtus strengthened the authority of the papacy in southern Italy by military expeditions, and restored several buildings within the city of Rome. During preparations for a crusade he died in Rome on the 13th or 14th of December 1124.
See M. Maurer, Pabst Calixt II. (Munich, 1889); U. Robert, Hisloire du pape Calixte II. (Paris, 1891); and A. Hauck's Realencyklopädie, Band iii. (Leipzig, 1897).
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)