The Roman Cosmos
It is the Pantheon, perhaps, that best stands for the crowning moment of the Roman Empire. It faced north toward the incoming traffic of the coastal highway, the Via Fla-minia. The approach was commonplace: a closed forum, long and narrow, at the south end of which rose a standard temple front.
But passing through this porch of smooth monolithic columns of Egyptian granite, one entered a mighty domed rotunda, 150 Roman feet (43 meters) both in height and diameter, that enclosed a vast,
unob-
structed, thoroughly ordered space suffused with the even light that shone through an oculus and the open bronze doors. (Fig.
217
10.4) The hemispherical concrete dome, with five diminishing rows of coffers verging toward the oculus and harboring gilded bronze rosettes like gleaming stars, rested on a multicolored wall arranged in two sto-reys. Niches carved in the thickness of the wall, each screened by two columns of colored marble and flanked by pilasters, alternated with smal tabernacles or "temple fronts," which stood in front of the wall plane and were crowned by segmental and triangular pediments. At the entrance niche and the apse across the way, the screening columns were omitted.
The apse semi-
dome and the barrel vault over the entrance lifted their arc into the second sto-rey. This second storey was actually a broad frieze of blind windows and triplets of tall thin panels patterned with colored mar-bles. The floor was paved with disks and squares of granite, marble, and porphyry set in a grid that was aligned with the main north-south dire tion of the building and reflected the grid armature of the coffering overhead.
The easy grace of this superb interior is entirely deceptive. Behind the tapestry of Classical niches and precious stones that wraps around the rotunda is a tremendously thick wall, 6 meters or 20 Roman feet across, which is what really supports the approximately 5,000 tons of weight exerted by the dome. The relationship of load and support is not direct. The wall, rather than being solid, has been riddled with stacked chambers. These chambers helped to hasten the drying process of the concrete, and