Two side chapels lie off the main crossing of the cathedral. The Cappella del Corporale, on the north side, was built between 1350 and 1356: it is two bays deep, with quadripartite vaults, decorated by Ugolino and his workshop, 1357-1364. The left wall depicts various miracles performed by communion wafers throughout the ages, and the right wall, the Miracle of Bolsena. In 1263, a young priest who doubted the miracle of transubstantiation -- the transformation of the communion wafer and wine into the actual body and blood of Christ -- was saying mass at Bolsena, on the shores of a lake a few dozen miles south of Orvieto. As he raised the Host toward the heavens, it began dripping blood onto the corporale (cloth covering the altar). The altar cloth instantly became a relic and was rushed to Pope Urban IV, who proclaimed the feast day of Corpus Christi. The relic resides in a huge gilded silver case designed in 1339 to mimic the cathedral facade and set with scenes of the Miracle of Bolsena and life of Christ in enameled panels inlaid with silver.