I just was browsing wikimedia commons and I found this really great image from the Hagia Sophia that I had to add.
It was not an unreasonable demand in the circumstances. The Sassanids were perennially at war with Rome. Christians were now suspected for potential treachery. The "Great Persecution" of the Persian Christian churches occurred in a later period, 340-363, after the Persian Wars that reopened upon Constantine's death. In 344 came the martyrdom of Catholicos Shimun bar Sabbae, with five bishops and 100 priests.
===Was Constantine a Christian?===
The religion of Constantine the Great, while generally assumed to be Christian in view of his pro-Christian policies, is disputed by some secular historians.