The Pantheon (Latin Pantheon, from Greek Pantheion, meaning "Temple of all the Gods") is a building in Rome which was originally built as a temple to the seven deities of the seven planets in the state religion of Ancient Rome, but which has been a Christian church since the 7th century. It is the best-preserved of all Roman buildings and the oldest important building in the world with its original roof intact. It has been in continuous use throughout its history.

The building is circular with a portico of three ranks of huge granite Corinthian columns (eight in the first rank and two groups of four behind) under a pediment opening into the rotunda, under a coffered, concrete dome, with a central opening (oculus), the Great Eye, open to the sky. A rectangular structure links the portico with the rotunda. 

The large bronze doors to the cella, once plated with gold, still remain, but the gold has long since vanished. The pediment was decorated with a sculpture in bronze showing the Battle of the Titans - holes may still be seen where the clamps which held the sculpture in place were fixed.  The height to the oculus and the diameter of the interior circle are the same, 43.3 metres (142.5 ft), so the whole interior would fit exactly within a cube (alternatively, the interior could house a sphere 43 metres (142.5 ft) in diameter).

The dome is the largest surviving from antiquity and was the largest dome in western Europe until Brunelleschi's dome of the Duomo of Florence was completed in 1436. It was covered with gilded bronze plates. The interior of the roof was probably intended to symbolize the arched vault of the heavens. The Great Eye at the dome's apex is the source of all light and is symbolic of the sun. Its original circular bronze cornice remains in position. The oculus also serves as a cooling and ventilation method. As wind passes over the dome of the Pantheon, it is accelerated and creates a negative pressure zone called the Venturi effect. This pulls air out of the oculus at the top of the dome, drawing more air in from the portico entrance. The interior features sunken panels (coffers), which originally contained bronze star ornaments. This coffering was not only decorative, but also reduced the weight of the roof, as did the elimination of the apex by means of the Great Eye.

It may be noted that the proportions of the building are in discord with the classical ideal. Most evident is the rather large pediment, which appears far too "heavy" for the columns supporting it. The reason for this was the expectation that the building would be much taller than it actually is, which would affect larger columns. However, by the time the pediment was built, it was realised that the supply of imported stone for the columns was not enough to build to its anticipated height, and thus the builders had to settle with a building that is somewhat out of proportion.