Diocletian was in Antioch in the autumn of 302, when the next instance of persecution occurred. The deacon Romanus visited a court while preliminary sacrifices were taking place and interrupted the ceremonies, denouncing the act in a loud voice. He was arrested and sentenced to be set aflame, but Diocletian overruled the decision, and decided that Romanus should have his tongue removed instead. Romanus would be executed on November 18, 303. The boldness of this Christian displeased Diocletian, and he left the city and made for Nicomedia to spend the winter, accompanied by Galerius.

Throughout these years the moral and religious didacticism of the emperors was reaching a fevered pitch; now, at the behest of an oracle, it was to hit its peak.

According to Lactantius, Diocletian and Galerius entered into an argument over what imperial policy towards Christians should be while at Nicomedia in 302. Diocletian argued that forbidding Christians from the bureaucracy and military would be sufficient to appease the gods, while Galerius pushed for their extermination. The two men sought to resolve their dispute by sending a messenger to consult the oracle of Apollo at Didyma. Porphyry may also have been present at this meeting.
Upon returning, the messenger told the court that "the just on earth" hindered Apollo's ability to speak. These "just", Diocletian was informed by members of the court, could only refer to the Christians of the empire. At the behest of his court, Diocletian acceded to demands for a universal persecution