The Pantheon is the best preserved and one of the most impressive of all Roman buildings. It was constructed in AD 118-128 during the reign of Emperor Hadrian. The Pantheon was a temple to all the Olympic Gods, and the word pantheon is Greek for ?of all the gods?. The Pantheon today is a remake of the original one, which was built by M. Vispanius Agrippa in 27 BC. A fire probably destroyed it. In AD 609, Pope Boniface VIII received the temple as a gift from the emperor of Byzantium. He converted it into a Christian church dedicated to Madonna and the martyrs. This is the reason for which it still stands today, avoiding destruction. The Pantheon is an immense round temple covered by a single dome, fronted by a transitional block and a traditional portico of eight Corinthian columns. The diametre of the hemispherical dome and cylinder is 43.2 metres. If the dome were a full sphere, the curve of the inner surface would just touch the floor; thus, a perfect sphere is contained, a symbolic reference to the temple?s dedication to all gods (pan (?all?) plus theos (?god?)=in the sphere of the heavens). Therefore, the dome has a radius of 26.6 metres and the cylinder has a height of 26.6 metres. The drum and dome are made of solid monolithic concrete, reinforced with bands of vitrified tile. The wall of the drum is 6.1 metres thick, and is hollowed out by a series of alternately rectangular curve niches or recesses. The only window in the building is a central oculus, 9.1 metres in diametre. Because the oculus is open to the sky, the floor is slightly concave with a drain at the center. The huge bronze doors (7 metres high) are the largest Roman doors to survive in place and remain in use. The portico is 33.5 metres in length and 18 metres deep.