 Placidi had a strong devotion to God and so after seeing his sisters married off chose almost at once to enter consecrated life as a simple friar and entered the Order of Friars Minor at the convent of Santissima Trinitá in 1665 while commencing his novitiate on 7 February 1667.He underwent his theological and philosophical studies in Viterbo.In 1683 - following the successful completion of his studies - he was ordained to the priesthood (he celebrated his first Mass in Velletri) and was at once appointed as the assistant master of novices in Orvieto.