Saint Callistus I of Constantinople lived an ascetic life in Mount Athos, at the Skete of Magoula, under the guidance of Saint Gregory of Sinai. He stayed there for twenty-eight years, after which, in 1350, he was elected Patriarch of Constantinople.
The saint was distinguished for his virtues and grace. After four years on the patriarchal throne, he withdrew to the Holy Monastery of Saint Mamas in Constantinople, where he remained until 1355, when he again assumed the patriarchal office.
Among other, Saint Callistus was sent to the Serbian Queen Helen in order to draw the Serbian people closer to the Church and to teach the word of the Gospel.
However, he fell gravely ill and completed his earthly life in the city of Serres. He was buried in a magnificent chapel at the Metropolitan Church of Saints Theodore in Serres.
He was recognized for his venerable life and charismatic personality. His name is recorded in the monachologion of the Holy Monastery of Iviron, where he lived for a considerable time. He is also regarded as one of the most important representatives of the hesychastic tradition of Mount Athos.
