St. Peter Celestine was founder of the Celestine Order. He was living in a mountain solitude when he was called to Rome by his election to the Pontificate. He was accused of excessive simplicity in public affairs, nor did he deny the truth of this accusation. Other Popes, such as Sts. Martin and Benedict IX had resigned the Papacy; the Thirteenth Century canonists nevertheless, disputed whether it was lawful for the Supreme Pontiff ever to renounce his position.
Celestine V decided the question according to primitive Roman tradition, and laid aside the papal robes to return to his former monastic life. Both during his pontificate and after his humble abdication, he worked many miracles. He died May 19, 1296.
(Source: The New Roman Missal by Father Lasance).