In Chapter II of his Folklore Studies, ancient and modern, Sir William Halliday gave a translation of a Byzantine carol in honour of St. Basil the Great, and with this a full discussion of the legend celebrated in the carol. This is a story of a contact between the emperor Julian the Apostate in his last campaign against Persia and St. Basil, and how Julian's death was brought about by the agency of St. Mercurius, a soldier who was martyred in the Decian persecutions. The legend is recorded in the life of St. Basil attributed to St. Amphilochius, Bishop of Iconium, and in this life it appears we may see the start of the whole story. The supposed author was a contemporary of St. Basil, but the document is rejected as apocryphal, and appears to be of the eighth or ninth century, a date which allows plenty of time for the accumulation of legend about a name so well known in Asia Minor as that of the great bishop of Caesarea. Sir William Halliday has translated the relevant passages: for convenience I here give a very brief summary of the parts of the story which most closely touch the carol.
The emperor Julian on his way to his campaign in Persia met Basil somewhere in the neighbourhood of Caesarea. Basil offered the emperor three loaves; angry at the smallness of the gift, the emperor sent him some hay in return; further angered by the fact that this gift gave the saint the right of pasturage on a certain meadow, he threatened on his return to destroy the city. Basil gathered his flock together, and they went to pray in the church of the Virgin on ‘Mount Didymus.’ The Virgin appeared, and called for the warrior Mercurius, who should go to Persia and slay Julian. Basil then went to the shrine of St. Mercurius, and found that the body was not there. This he announced to the people, and in seven days came the news of the death of Julian. Such very briefly is the legend as recorded in the Amphilochian life.