The Lost Octagons of the Pantheon: Images and Evidence

In antiquity, a series of three barrel vaults, each one of a different material, covered the passage into the Pantheon rotunda. The first of these vaults, made of metal, hung from the bronze beams that once supported the portico roof.1 Probably removed by medieval plunderers, this vault is long gone and no drawings or other images record its appearance.2 But the second vault still stands over the main door, and its square-coffered masonry appears virtually unchanged in the various repre sentations of it made since the sixteenth century.3 On the other side of the door, the interior entrance alcove of the Pantheon cuts through the thick cylindrical perimeter wall of the rotunda, creating an area of transition between the lower, darker space of the portico and the high, bright space under the dome. Above it, the third and final barrel vault is also still present today (Fig. i). Although the brickwork of its intrados is mostly exposed, with white marble veneer only at the edges, several sixteenthand seventeenth-century representations of the Pantheon imply that it was once covered by an ornamental pattern of octagonal and square coffers. The octagons are discernible, for example, on the ruin of the Pantheon depicted in Jean Lemaire's painting of Theseus Finding his Father's Sword and Sandals (c. 1630), now in the Statens Museum in Copenhagen (Fig. 2a-b).4There the barrel vault of the exterior entrance alcove looks as it does now, with a square coffer that echoes those set into the dome, but the barrel vault of the interior alcove, on the left, has octagonal coffering that cannot be seen today.