An irregular complex of many buildings seen beyond the colonnade on the right side of the Basilica of St. Peter's. Today, the residence of the Pope, who, before Gregory XI's return from Avignon in 1377, had lived officially at the Lateran Palace. The original Vatican apartments erected first in the fifth century were used only for the reception of foreign soveriegns visiting Rome. Additions were made to the imposing building begun in 1450 by subsequent pontiffs. Pope Sixtus IV (reigned 1471-84) added the Sistine Chapel in 1473, named after him; Pope Alexander VI (reigned 1492-1503) the Appartamento Borgian; and Innocent VIII (reigned 1484-92) the Belvedre; Julius II (reigned 1503-13) the Logge, and he also laid the foundations for the Vatican Museums. Some of the greatest architects and painters of the times were employed—Bramante, Michelangelo, Raphael, Sangallo, Maderna, Bernini, and others—to make it the largest palace in the world. It has eighty impressive staircases and several thousand rooms, few of which are actually used as papal apartments. Museums, library, picture gallery, collections, Sistine Chapel, galleries, stanzas, loggias also occupy the immense edifice called the Vatican.