Callistus II of Constantinople
Callistus II Xanthopoulos or Xanthopulus was a Byzantine Hesychast monk and spiritual writer who reigned as Ecumenical Patriarch of Constantinople in 1397. He was Patriarch through the reign of the Byzantine Emperor Manuel II Palaiologos, and through his short Patriarchal reign Constantinople was under siege by the Ottoman Sultan Bayezid I.
His surname indicates that he was from the monastery of Xanthopoulos. With another monk, Ignatius Xanthopoulos, Callistus composed the important Century, a tract of 100 sections on the ascetical practices of the Hesychastic monks; it was incorporated in the Philokalia of Nicodemus the Hagiorite and had a great influence on Orthodox spirituality. The majority of Patriarchs in the 14th century were monks in the Hesychast tradition. Within the Orthodox Church, his memory is celebrated on 22 November.
