Pope John I inherited the Arian heresy, which denied the divinity of Christ. Italy had been ruled for 30 years by an emperor who espoused the heresy, though he treated the empire’s Catholics with toleration. His policy changed at about the time the young John was elected pope.
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 negotiations—designed 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.