Pope John I was the bishop of Rome from 13 August 523 to his death on 18 May 526. He was a native of Siena, in Italy. Pope John I played a pivotal role in standardizing how the Western Church calculated the date of Easter, with the help of the monk Dionysius Exiguus, in 525. He was sent on a diplomatic mission to Constantinople by the Ostrogoth King Theoderic to negotiate better treatment for Arians. Although John was relatively successful, upon his return to Ravenna, Theoderic had him imprisoned for allegedly conspiring with Constantinople. The frail pope died of neglect and ill-treatment.

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