The Pantheon is a building in Rome, Italy, commissioned by Marcus Agrippa during the reign of Augustus (27 BC – 14 AD) and rebuilt by the emperor Hadrian about 126 AD.
The building is circular with a portico of large granite Corinthian columns (eight in the first rank and two groups of four behind) under a pediment. A rectangular vestibule links the porch to the rotunda, which is under a coffered concrete dome, with a central opening (oculus) to the sky. Almost two thousand years after it was built, the Pantheon’s dome is still the world’s largest unreinforced concrete dome. The height to the oculus and the diameter of the interior circle are the same, 43.3 metres (142 ft).
It is one of the best-preserved of all Ancient Roman buildings. It has been in continuous use throughout its history, and since the 7th century, the Pantheon has been used as a church dedicated to “St. Mary and the Martyrs” but informally known as “Santa Maria Rotonda”.
The interior of the dome was possibly intended to symbolize the arched vault of the heavens. The oculus at the dome’s apex and the entry door are the only natural sources of light in the interior. Throughout the day, the light from the oculus moves around this space in a reverse sundial effect. The oculus also serves as a cooling and ventilation method. During storms, a drainage system below the floor handles the rain that falls through the oculus.
The dome features sunken panels (coffers), in five rings of 28. This evenly spaced layout was difficult to achieve and, it is presumed, had symbolic meaning, either numerical, geometric, or lunar. In antiquity, the coffers may have contained bronze stars, rosettes, or other ornaments.
Circles and squares form the unifying theme of the interior design. The checkerboard floor pattern contrasts with the concentric circles of square coffers in the dome. Each zone of the interior, from floor to ceiling, is subdivided according to a different scheme. As a result, the interior decorative zones do not line up. The overall effect is immediate viewer orientation according to the major axis of the building, even though the cylindrical space topped by a hemispherical dome is inherently ambiguous. This discordance has not always been appreciated, and the attic level was redone according to Neoclassical taste in the 18th century.Wikipedia