Siena Cathedral is one of the major artistic monuments of the late Middle Ages in Italy, and its Museum, which for more than a century has been the custodian of the priceless art works that were once in the cathedral, preserves the evidence of its artistic, devotional, and religious significance. In the Baptistery, the suggestive decoration of the ceiling illustrates the articles of the Apostles' Creed, which explicates in the three persons of the Holy Trinity the profession of faith requested of catechumens to be admitted to the sacrament of Baptism. The most recent great discovery is the Crypt, a unique thirteenth-century space brought to light in 2000 after more than seven centuries of oblivion. On its walls are frescoes painted between 1270 and 1280, visible now in all the splendor of their original colors. Last but not least is the sixteenth-century Oratory of San Bernardino and the adjacent Diocesan Museum of Sacred Art.