Blessed Pietro Casani (8 September 1570 – 17 October 1647) was an Italian Roman Catholic priest and a professed member of the Piarists.
He became an assistant and a close personal friend of Saint Giuseppe Calasanz.
Casani had assumed the religious name of "Pietro della Natività di Maria" upon his solemn profession and had once been part of the Congregazione della Beata Vergine Maria that Saint Giovanni Leonardi founded.Casani served in numerous roles of leadership within the Piarists due to being a close assistant to Calasanz and travelled across the Italian peninsula for visitations of various houses while living in Rome and Naples as part of his duties.
He was an advocate for the religious of the order being poor and moved to the Piarists from Leonardi's for that exact reason.His beatification cause commenced on 22 March 1922 - under Pope Pius XI and he became titled as a Servant of God: the first stage in the sainthood process.
He was made Venerable in 1991 and Pope John Paul II beatified him in Saint Peter's Square on 1 October 1995.