In 862, the Sclavonic princes of Pannonia, Rostislaw, Swaetopolk, and Kotel requested the emperor Michael and the patriarch Photius, to send them teachers, "because they were without true instructors for the people," and they desired to have instruction and divine worship in their own language. It appears that missionaries of the Latin Church had already penetrated amongst them, but probably had been unable to master the Sclavonic tongue; at any rate, the Pannonians refused to accept them, and turned instead to the East.
None were better calculated to execute this mission than the brothers Methodius and Cyril, the former of whom had for some years governed a Sclavonic province, and both had been born at Thessalonica, on the confines of Sclavonic peoples, and where the language was familiar to the natives. The emperor and the patriarch felt this, and sent for them, and laid before them the desire of these heathen princes for the Gospel. The brothers at once undertook the mission, and set forth. On their way, Methodius was the means of converting the king of the Bulgarians. Boris had a sister, who was a Christian, having been brought up at Constantinople, whither she had been carried captive. The prince, who was passionately fond of hunting, desired the emperor to procure him a picture, which should illustrate his favourite pursuit, and adorn the hall of a new palace he had erected. Methodius was commissioned by the emperor to execute this task, and he appeared before king Boris, not as a missionary, but as a painter. "Let it be a good picture," said the prince, "large and terrible." "So shall it be," answered Methodius, "but one thing I demand,--that I may be left undisturbed here to complete my picture, that no one may see it till it is finished." The king reluctantly gave his consent, and day after day passed, and the painter was not seen. He remained closely shut up within the palace. Weeks rolled by, and Boris chafed with impatience and curiosity. At length the doors were thrown open, and the king entered. Methodius had painted the Last Judgment on the wall of the new hall. Above sat Christ on the great white throne, and below were men receiving sentence, and the angels dividing them. An awe and wonder fell on the king's heart as he contemplated the picture. "What meaneth this?" he asked. And Methodius seized the opportunity of preaching to him righteousness, temperance, and judgment to come. He explained to the king the whole doctrine of the final judgment of men, their fate depending on their works in this world, and the king trembled. He went on to speak of the glories prepared for the baptized who keep the faith. Great and purifying thoughts swelled the bosom of the prince, and going up to the painter, he said, with his head bowed, "Take me, and teach me, that I too may pass to the beautiful side of the picture."