chapel, subsidiary place of worship. It is either an alcove or chamber within a church, a separate building, or a room set apart for the purpose of worship in a secular building. A movable shrine containing the cappa, or cloak, of St. Martin was first called a cappella; hence a sanctuary that is not called a church. Though the churches of the early Middle Ages possessed only the single altar of the apse, chapels became necessary with the increase of relics and of devotions at altars sacred to numerous saints. At first they appeared as minor apses, flanking the main apse. After the 10th cent., in order to accommodate the increasing number of pilgrims, a complex series of radiating chapels was developed behind the high altar. In the 13th cent. chapels were added to the side-aisle bays of choir and nave. In England the strongly projecting transepts provided the favored space for a relatively small number of chapels. In France the Lady Chapel (dedicated to the Virgin) is the central chapel of the chevet and is sometimes larger than the others, while in England it occurs directly behind the high altar. Peculiar to English cathedrals are the small chantry chapels, mostly of the 14th and 15th cent., either built and endowed by individuals for their private Masses or serving to enclose the tombs of bishops and other churchmen. From the early Middle Ages, members of royalty had the right to an independent private chapel. Such are the separate building of the Sainte-Chapelle, Paris; St. George's Chapel at Windsor; and Henry VII's magnificent chapel at Westminster, London. In addition, there were royal mortuary chapels, the most celebrated being that of Charlemagne (796–804), at Aachen, since converted into a cathedral. Numerous lords of medieval castles and manor houses established private chapels, over which episcopal jurisdiction was enforced as completely as possible. The two main chapels at the Vatican are the Pauline Chapel (1540), designed by Antonio da Sangallo for Paul III, and the Sistine Chapel (1473), built by Sixtus IV and celebrated for its great fresco decorations by Michelangelo and other masters. Two of the most famous French modern chapels (built in the 1950s) are the chapel at Vence designed by Henri Matisse and the one at Ronchamp by Le Corbusier; both are freestanding buildings.