Since the fourth century, the highest places in churches, usually covered with domes or conches, have symbolized the celestial realm. Although the subsequent rebuilding of the apse at Orvieto into a more stable square space thwarted the possibility for a rounded conch, the vault of the Cappella Maggiore serves a corresponding purpose (Figure 13.1). As previously mentioned, whereas in most fourteenth-century mural programs, the groin vaults allude to heaven, at Orvieto, the Marian narrative extends into the vault to depict heaven – a hierarchical arrangement more common to Byzantine programs.