This signifies, in general, those periods of time specifically set apart for spiritual contemplation, religious devotions, and inward renewal. Participants usually seclude themselves from their normal occupations. The practice is not uniquely Christian, but Christians have drawn inspiration from the examples of Jesus praying in the desert (Matt. 4), and from the apostles tarrying in the upper room before Pentecost (Acts 1:13,14). Ignatius Loyola fully developed a complete, practical method of retreat in his volume Exercitia spiritualia, approved by Paul III in 1548. Taking inspiration from the Jesuits, Roman Catholic retreat houses have sprung up in phenomenal numbers around the world. Canon law obligates all priests to attend one retreat every three years and members of all religious orders to attend at least one each year. Retreats are not, however, limited to the Roman Catholic Church. They were practiced in the* and adopted formally by the in 1856. Keith Miller, director of Laity Lodge in Texas, has given the retreat method of spiritual renewal great impetus in the USA since 1961.