He became a follower of Girolamo Savonarola, attending his sermons and studying his writings, and eventually Bernardino himself began preaching in the public squares of Florence.
According to the Florentine chronicler Bartolomeo Cerretani, about twenty adherents of Savonarola formed a secret society and elected Peter pope.
In 1502 the members left the town secretly and proceeded to Mirandola where Count Gian Francesco, a zealous supporter of Savonarola, gave them a friendly reception.
When, a little later, the count was besieged by two of his brothers, who claimed Mirandola, Peter declared it God's will that Gian Francesco should overcome his enemies.
The sectaries fell into the hands of the victors, Peter and some of his companions were burned as heretics; the remainder were expelled or dispatched to Florence.