When the eastern emperor began imposing severe measures on the Arians of his area, the western emperor forced John to head a delegation to the East to soften the measures against the heretics. Little is known of the manner or outcome of the negotiationsdesigned to secure continued toleration of Catholics in the West.
When John returned to Rome, he found that the emperor had begun to suspect his friendship with his eastern rival.
On his way home, John was imprisoned when he reached Ravenna because the emperor suspected a conspiracy against his throne. Shortly after his imprisonment, John died, apparently from the treatment he had received.