Endowed with holy relics and forming the primary locus of the Christian mass, the altar occupied the center of the lavish architectural and visual programs that comprised medieval church buildings from the fourth century onward.  Whereas triumphal arches, covered with mosaic images, had framed the space of the altar in Early Christian basilicas, and free-standing cult statues and reliquaries had come to personalize altars in twelfth-century pilgrimage churches, the end of the thirteenth century witnessed the rise of what would become the dominant field of ritual spectacle and artistic innovation in the Renaissance: the altarpiece. Painted, sculpted, or both; often outfitted with multiple hinged panels that could be opened and closed; supported by predellas that housed relics; and, in turn, bearing delicate micro-architectural armatures that surged toward the heavens, late medieval altarpieces were multimedia installations meant to provide a suitably splendid backdrop for the Eucharistic liturgy and to convey sacred truths to large congregations.  They also became the testing ground for master craftsmen – woodcarvers, painters, and carpenters – who transformed their religious commissions into dazzling displays of technical virtuosity.