Pantheon

    The portico consists of three rows of eight columns, 46 feet high of Egyptian granite with Corinthian capitals. They support an entablature facing the square, which bears the famous inscription in Latin, attributing the construction to Agrippa, although the extant temple was rebuilt later by Hadrian.

    The dome has a span of 142 feet, the largest dome until Brunelleschi's dome at the Florence Cathedral of 1420-36.

    The interior volume is a cylinder above which springs the half sphere of the dome. A whole sphere can be inscribed in the interior volume, with the diameter at the floor of the cylinder of 143 feet equaling the interior height.

    Five rows of twenty-eight square coffers of diminishing size radiate from the central unglazed oculus with a diameter of 29 feet at the top of the dome.

    The dome is constructed of stepped rings of solid concrete with less and less density as lighter aggregate (pumice) is used, diminishing in thickness to about 4 feet at the edge of the oculus. The dome rests on a cylinder of masonry walls 20 feet. Hidden voids and the interior recesses hollow out this construction, so that it works less as a solid mass and more like three continuous arcades which correspond to the three tiers of relieving arches visible on the building exterior. Originally, these exterior walls were faced with colored marbles.