Withdrawal for a period of time form one's usual surroundings and occupation to a place of solitude for meditation, self-examination, and prayer, in order to make certain necessary decisions in one's spiritual life. Although the practice is older than Christianity, the example of Christ's forty days in the desert makes such retreats part of divine revelation, to be imitated, as far as possible, by his followers. As a formal devotion among all classes of the faithful, retreats were introduced with the Counter-Reformation, led by St. Ignatius of Loyola, and followed by St. Francis de Sales and St. Vincent de Paul. Retreats for a specified number of days are required of all priests and religious. "We desire," wrote Pope Pius XI, "that retreat houses, where persons withdraw for a month, or for eight days, or for fewer, to put themselves into training for the perfect Christian life, may come into being and flourish everywhere more numerously" (Constitution Declaring St. Ignatius Patron of All Spiritual Exercises, July 25, 1922).