Pantheon is a temple in Rome, dedicated to "all the gods" (that's what the word Pantheon means in Greek), in particular those associated with the family of the Julio-Claudians. The Pantheon is one of the best preserved buildings of the ancient world, and it remains in almost it's original form.
The Construction of Pantheon begun in 27 BC by the statesman Marcus Vipsanius Agrippa, probably as a building of the ordinary classical temple type--rectangular with a gabled roof supported by a colonnade on all sides. It was completely rebuilt by the emperor Hadrian sometime between AD 118 and 128, after it was destroyed by fire (fires were not uncommon those days). Some alterations took place in the early 3rd century by the emperor Lucius Septimius Severus and Caracalla.
It is a big building of concrete faced with brick, with a great concrete dome rising from the walls and with a from porch of Corinthian columns supporting a gabled roof with triangular pediment. Beneath the porch are huge bronze double doors, 7m high, the earliest-known large examples of this type. The Pantheon is remarkable for its size, its construction, and its design. The dome was the largest built until modern times, measuring about 43m in diameter and rising to a height of 22m above its base. There is no external evidence to brick arch support inside the dome, except in the lowest part, and the exact method of construction has never been determined. Two factors, however, are known to have contributed to its success: the excellent quality of the mortar used in the concrete and the careful selection and grading of the aggregate material, which ranges from heavy basalt in the foundation of the building and the lower part of the walls, through brick and tufa (a stone formed from volcanic dust), to the lightest pumice toward the center of the vault. In addition, the uppermost third of the drum of the walls, seen from the outside, coincides with the lower part of the dome, seen from the inside, and helps contain the thrust with internal brick arches. The drum itself is strengthened by huge brick arches and piers set above one another inside the walls, which are 6m thick.
The porch is conventional in design, but the body of the building, an immense circular space lit solely by the light that floods through the 27-foot (8-metre) "eye," or oculus, opening at the center of the dome, was revolutionary possibly, this was the first of several great buildings of antiquity that were designed to favor the interior rather than the exterior. In contrast with the plain appearance of the outside, the interior of the building is lined with colored marble; the walls are marked by seven deep recesses, screened by pairs of columns whose modest size gives scale to the immensity of the rotunda. Rectangular coffers, or indentations, were cut in the ceiling probably under Severus and decorated with bronze rosettes and molding. Pope Boniface VIII received the building as a gift from the emperor of Byzantium, and the Pantheon was dedicated as the Church of the Santa Maria Rotonda, or ad Martyres, which it remains today. Thanks to it, the Pantheon remains untouched and in it's closest-to-original form.