10/09/2026
St. John Leonardi’s Temporary Union with the Piarists
St. John Leonardi, patron of pharmacists and founder of the Clerics Regular of the Mother of God (Leonardini), had a brief union with the Piarists (the Clerics Regular of Saint Joseph Calasanz). His feast day is October 9. He was a zealous Italian apostle, founded the congregation of the Mother of God, whose priest-members traveled throughout Tuscany urging the people to a stronger interest in their religion. Fr. John Leonardi longed to convert pagans, but his spiritual director, St. Philip Neri, told him to remain in Italy. So instead he founded a seminary in Rome to train young men for the priesthood from all the mission lands.
According to historical accounts, Pope Paul V issued a papal decree on January 14, 1614 approving the union of the Lucca Fathers (Leonardini) with the Piarists.
This was part of a broader effort to strengthen religious congregations during the Counter‑Reformation. The union was temporary, intended to last only until the beginning of 1617. When that date arrived, Paul V issued another decree formally constituting the Piarists as a separate congregation, ending the union . This meant the Leonardini continued as their own order, while the Piarists became an independent religious congregation.