The Saint of the Day for May 18 is St. John I.
This Tuscan was destined to be glorified not only during his lifetime but after his death as well. Although peace with the East had been restored, a suspicious Theodoric grumbled in his castle at Ravenna. An Arian, the king saw the new friendliness between East and West as a serious threat to his reign. To further alarm him, Emperor Justin had reinstated the laws against heretics, Arians included, and had embarked on a campaign of confiscating churches and excluding heretics from public office, causing many Arians to abandon their faith. Infuriated, Theodoric summoned John to Ravenna and ordered him to head a delegation to the orthodox emperor to ask that the persecution stop and allow forced converts to return to Arianism. At first John refused, then fearing that the king's wrath 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. The day of Easter, 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. The aged pope was spent; the prospects before him were dismal. Already ailing, Pope John died and was hastily buried outside the castle walls. Pope John's body was exhumed and on May 27, 526, was returned to Rome and placed in the nave of St. Peter's.
— Excerpted from The Popes: A Papal History, J.V. Bartlett