27 a.C. - 124 d.C.

The Pantheon (UK: /ˈpænθiən/, US: /-ɒn/; Latin: Pantheum, from Greek Πάνθειον Pantheion, 
"[temple] of all the gods") is a former Roman temple and since 609 AD, 
a Catholic church (Basilica di Santa Maria ad Martyres or Basilica of St. Mary and the Martyrs), 
in Rome, Italy, on the site of an earlier temple commissioned by Marcus Agrippa during the 
reign of Augustus (27 BC – 14 AD). It was rebuilt by the emperor Hadrian and probably 
dedicated c. 126 AD. Its date of construction is uncertain, because Hadrian chose not to 
inscribe the new temple but rather to retain the inscription of Agrippa's older temple, 
which had burned down.

The building is cylindrical 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 metres (142 ft).

It is one of the best-preserved of all Ancient Roman buildings, in large part because it has 
been in continuous use throughout its history: since the 7th century, it has been a church 
dedicated to St. Mary and the Martyrs (Latin: Sancta Maria ad Martyres) but informally known 
as "Santa Maria Rotonda".[5] The square in front of the Pantheon is called Piazza della Rotonda. 
The Pantheon is a state property, managed by Italy's Ministry of Cultural Heritage and Activities 
and Tourism through the Polo Museale del Lazio. In 2013, it was visited by over 6 million people.

The Pantheon's large circular domed cella, with a conventional temple portico front, was unique 
in Roman architecture. Nevertheless, it became a standard exemplar when classical styles were 
revived, and has been copied many times by later architects.