The Pantheon, a harmonious balance of both Roman engineering genius and Greek aesthetics, is completed in 128.
A a rectangular forum in front of the temple softens the ungainly juxtaposition of its three sections: an immense round temple, covered by a single hemispherical dome, fronted by a transitional block and a traditional temple portico of eight Corinthian columns carrying a triangular pediment.
Deceptive in its simple appearance, the Pantheon consists of a circular drum carrying a hemispherical dome with an inside diameter of 142 feet (43.2 meters).
The drum and dome, made of solid monolithic concrete, are reinforced with bands of vitreous tile, with relieving arches incorporated in the concrete to collect and distribute the vertical gravity loads to the drum.
A series of alternately rectangular and curved niches or recesses hollow out the drum’s 20 foot-thick (6.1 meter) wall, thus transforming the drum into a series of massive radial buttresses that reduce its deadweight without decreasing its strength.
The density of the filler in the concrete, from pumice in the upper dome to tufa in the middle sections and dense basalt in the foundations, lessens the weight of the upper sections, and thus the magnitude of the thrusts.
The curve of the dome’s inner surface, if extended to the floor, would just "kiss" the floor; thus containing, in symbolic reference to the temple's dedication to all the gods in the sphere of the heavens, a truly perfect sphere.
Deep coffers radiate down from the thirty foot-diameter (9.1 meter) central oculus—the building’s only window—to lessen the visually compressive effect of the dome on the inside.
Because the oculus is open to the sky, the floor is slightly concave with a central drain.
Ornamented by marble revetments, mosaics, and stuccowork, the temple features enormous bronze doors twenty-four feet (seven meters) high (the largest Roman doors to survive in place and remain in use).
