The Pantheon originally built by Marcus Agrippa as a temple to all the gods of Ancient Rome, and rebuilt in the early 2nd century AD.

The intended degree of inclusiveness of this dedication is debated. The generic term pantheon is now applied to a monument in which illustrious dead are buried. 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) open to the sky.

The Pantheon is the oldest large-scale dome in Rome. The height to the oculus and the diameter of the interior circle are the same, 43.3 metres (142 ft). A rectangular structure links the portico with the rotunda. It is one of the best preserved of all Roman buildings. It has been in continuous use throughout its history. Since the 7th century, the Pantheon has been used as a Roman Catholic church dedicated to "St. Mary and the Martyrs" but informally known as "Santa Maria Rotonda."