When the eastern emperor, Justin, began imposing severe measures on the Arians of his area, the western emperor forced Pope John to head a delegation to the East to soften the measures against the Arians. At first John refused, but then fearing that the king's anger would be taken out on Western Catholics, he agreed to do Theodoric's bidding on every count save one. He boldly told the king that he would not ask the emperor to allow converts to return to heresy.
The pope arrived in Constantinople shortly before Easter in 526, and since he was the first pope to leave Italy, his reception was more than he could have dreamed. He had been met by the entire city at the twelfth milestone, where the clergy led the procession carrying candles and crosses, and even the emperor prostrated himself before the Holy Father. On the day of Easter, Pope John was seated in a throne higher than the one occupied by the patriarch, in the church of Sancta Sophia, where he celebrated Mass in the Latin tradition. John was accorded the highest honor when he placed the customary Easter crown on the head of Emperor Justin.
After meeting with Justin on Theodoric's behalf, the pope made the exhausting trip back to Ravenna. The king's fury raged. Jealous of the pope's grand reception in the East, Theodoric accused the pope of failing his mission by not securing all of the demands put to Justin. The king then ordered John to remain in Ravenna at his disposal.
John was imprisoned when he reached Ravenna because the emperor suspected a conspiracy against his throne. Shortly after his imprisonment, John died, and because of the cruel treatment he had received, he is counted as a martyr for the faith.
O Almighty God, by whose grace and power thy holy Pope and Martyr St. John triumphed over suffering and was faithful even unto death: Grant us, who now remember him with thanksgiving, to be so faithful in our witness to thee in this world, that we may receive with him the crown of life; through Jesus Christ our Lord, who liveth and reigneth with thee and the Holy Spirit, one God, for ever and ever. Amen.