from the Synaxarion:
The Holy Martyr John Kalphes lived in a suburb of Constantinople, called Galata. By profession he was an architect and in his craft he had acquired great mastery, such that important officials made use of his services. He was entrusted with the inner adornment of the sultan's palace.
Saint John Kalphes was distinguished for his Christian charity, he concerned himself over orphans and about those locked up in prison, and many turned to him for help. One time a certain dignitary asked Saint John to take on his nephew as an apprentice. He agreed, and the youth (upon completion of his apprenticeship) received an honorable position at court. And one time, encountering his former teacher and benefactor, he began to question Saint John, as to what it says in the Christian books about the "prophet" Mahomet. Saint John did not want to answer his question, but in light of the persistent demands of the youth, he declared the falseness of Mahometanism. The youth, devoted to Islam, reported this to the sultan's court, that the architect had insulted Mahomet. They brought Saint John to trial, where they demanded that he renounce Christ, but he bravely confessed his Orthodox faith. After torture, they sent the holy martyr off to penal servitude, where he spent 6 months. He was then routinely beaten for a period of three months in the prison and then, finally, on 26 February 1575, they beheaded him in the crowded city-square in Ergat-Bazara, near Bezstan. The sufferings of the holy Martyr John Kalphes were recorded by a steward of the Constantinople Patriarch, Andrew, who communed him with the Holy Mysteries in prison.