CALIXTUS II. (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 Feb. 1119 he was chosen pope at Cluny, succeeding Gelasius II., and in opposition to the anti-pope Greg ory VIII., who was in Rome. Soon after his consecration he opened negotiations with the emperor Henry V., to dispose of the dispute over investiture. Terms of peace were arranged, but at the last moment difficulties arose and the treaty was abandoned; and in Oct. 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 en thusiasm in the city, while Gregory having fled to Sutri, was de livered 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 Sept. 1122 was the result. He died in Rome on Dec. 13 or 14, 1124.