Concordat of Worms
Pope Callixtus II or Callistus II (c. 1065 – 13 December 1124), born Guy of Burgundy, was head of the Catholic Church and ruler of the Papal States from 1 February 1119 to his death in 1124. His pontificate was shaped by the Investiture Controversy, which he was able to settle through the Concordat of Worms in 1122.