Pantheon

The building is round in plan, except for the portico with 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, 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. The square in front of the Pantheon is called Piazza della Rotonda.

he 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

The Pantheon in the city of Rome is an Ancient Roman temple that was repurposed as a Catholic Church in the 7th century. The church was dedicated to “St. Mary and the Martyrs” and is commonly known as the “Santa Maria Rotonda.”  The original temple was constructed as early as the reign of Roman Emperor Augustus but was rebuilt several times, first by Trajan and finally completed by Hadrian in the year 126 A.D. The main building is famous because it has an opening at the top of its massive dome.