St Casimir was the son of the King of Poland. Trained from his youth in piety and learning, he sharply chastised his body with a hair-shirt and wore himself thin by frequent fasts.
The Passion of Christ was the constant subject of his meditations, and he never relaxed his spirit of prayer. He had great zeal for the propagation of the Catholic Faith and the suppression of the Ruthenian schism. Such was his charity and mercy to the poor and all sufferers that he won the name of father and defender of the needy.
He constantly preserved his virginity untarnished to the end of his life. Made perfect in a short time, and rich in virtues and merits, he foretold the day of his death and gave back his soul to God in the twenty-fifth year of his age. Leo XIII entered him, renowned for miracles, among the number of the saints.
– From: An Approved English Translation of the Breviarium Romanum, Burns & Oates, London, 1964