The Pantheon Basalt

Structure:
The exterior of the Pantheon, like its history, went through many metamorphoses. The porch of the old temple used to stairs since the construction later raised the ground level leading to the portico. The temple has a Greek facade that has a granite pediment that lies upon the giant Corinthian columns. Although the columns are not like the Greek ones that have drums: they are not segmented. The temple was originally framed by a colonnade and surrounded with other temples as well. The structure was built with with concrete and was once faced with marble. Basalt was used for its foundation; and pumice was used to build the building’s upper structure (Rickerson, 222). The building composed of a rectangular pronaos (portico) with

three lines of granite columns fronting a circular building designed as a huge hemispherical dome (43.3m in diameter), built over a cylinder of the same diameter and as high as the radius.

(Hannah, and Magli, 487). Many buildings surrounding the Pantheon, and the Pantheon itself was changed and ripped off. In 663, Emperor Constantinus II tore off the gilded bronze roof tiles of the Pantheon (Joost-Gaugier, 27). According to Rodolpho Lanciani, “Eugenius IV. lowered the rubbish accumulated against the portico, and paved the piazza and the adjoining streets. Urban VIII., having stripped the roof of the portico of its bronze beams (but no sooner the destruction was completed, he discovered that the alloy of the metal was not hard enough for casting guns), restored the east corner of the colonnade, and destroyed the shops built between the granite pillars. Alexander VII. put two columns from the baths of Nero (found in the Piazza di S. Luigi de' Francesi) in place of those missing, and pulled down some houses from which the canons of the Rotonda derived an income of 1500 scudi a year.” According to The Iconography of Sacred Space: A Suggested Reading of the Meaning of the Roman Pantheon, the exterior was originally covered with glittering gold in the form of gilded bronze tiles. Furthermore, Pope Clement XI commissioned Alessandro Specchi to add a high altar and apses the visitors

can see today.
Comparing to most churches that have a basilica plan, the Pantheon has a radial place that radiates outward. Unlike the Pantheon, the Basilica of San Vitale has an octagonal plan. Like many other churches (Hagia Sophia), the Basilica of San Vitale are full of circles (though its plan is more like a transition between circles and squares), symbolizing the eternal perfection – having no beginning nor end – and also the heaven (Grupico, 7). It is very interesting to see that the Pantheon and the Basilica of San Vitale’s plans are both inspired with geometric shapes, although the geometric shapes in the Pantheon is more about practical use in the structure, while the circles and squares of the basilica has its own holy meaning, and symbolism. In Early Christian period, the octagon became the symbol of resurrection of Jesus Christ (Grupico, 7). The exterior of the Basilica of San Vitale is made of bricks, taken from the ancient Roman buildings. Unlike the Pantheon with little windows, this church is covered with windows, which is extremely important for the mosaic-filled interior. The structure of the church is a beautiful combination between Roman architecture and the Byzantine architecture: polygonal plans, capitals, narrow bricks, the dome, vaults, etc. According to Alan H. Hayes, it is widely accepted that central-plan church evolve from Roman baths, and the basilical churches evolves from the basilica of the Roman, the courts of law.

2.

Material:
The Pantheon and the Basilica of San Vitale both have their own material, having the iconic material of their time: Roman and Byzantine.
The Pantheon was a Roman concrete structure. Roman concrete is a mixture of lime and volcanic ash (pozzolana, found near modern-day town Pozzouli). Roman concrete is also called hydraulic cement-based concrete. It is known for curing relatively rapidly, even in damp condition, thus it could be used for massive construction. The most daring thing about the use of Roman concrete in the Pantheon is that Portland cement needs steel reinforcement due to tendency of cracking caused by tension forces, meanwhile the Pantheon did not. The Pantheon still stands today is because of its special structure.
The Basilica of San Vitale was built with thin bricks with thick mortar joints, a typical example of Byzantine architecture (Rickerson,

262).