Pope John I (Latin: Ioannes I. 470 – 18 May 526) was Pope from 13 August 523 to his death in 526. He was a native of Siena (or the "Castello di Serena"), near Chiusdino, in Italy.
He is the first pope known to have visited Constantinople while in office. While a deacon in Rome, he is known to have been a partisan of the Antipope Laurentius, for in a libellus written to Pope Symmachus in 506, John confessed his error in opposing him, condemned Peter of Altinum and Laurentius, and begged pardon of Symmachus.
He may also be the "Deacon John" to whom Boethius, the 6th-Century philosopher, dedicated three of his five religious tractates, or treatises, written between 512 and 520.
John was very frail when he was elected to the papacy as Pope John I. Despite his protests, Pope John was sent by the Arian King Theodoric the Great--ruler of the Ostrogoths, a kingdom in present-day Italy--to Constantinople to secure a moderation of a decree against the Arians, issued in 523, of Emperor Justin, ruler of the Byzantine, or East Roman, Empire. King Theodoric threatened that if John should fail in his mission, there would be reprisals against the orthodox, or non-Arian, Catholics in the West. John proceeded to Constantinople with a considerable entourage: his religious companions included Bishop Ecclesius of Ravenna, Bishop Eusebius of Fanum Fortunae, and Sabinus of Campania.
Although John was successful in his mission, when he returned to Ravenna, Theodoric"s capital in Italy, Theodoric had John arrested on the suspicion of having conspired with Emperor Justin.
John was imprisoned at Ravenna, where he died of neglect and ill treatment. His body was transported to Rome and buried in the Basilica of Saint Peter.
The Liber Pontificalis credits John with making repairs to the cemetery of the martyrs Nereus and Achilleus on the Via Ardeatina, that of Saints Felix and Adauctus, and the cemetery of Priscilla. Pope John I is depicted in art as looking through the bars of a prison or imprisoned with a deacon and a subdeacon.
He is venerated at Ravenna and in Tuscany.
His feast day is 18 May, the anniversary of the day of his death (whereas it had formerly been 27 May).