The first Pantheon was constructed by Marcus Agrippa between 27-25 B.C. Between 118-125 A.D., Emperor Hadrian built a new Pantheon and, in 609, it was consecrated as the Church of Santa Maria ad Martyres under Pope Boniface IV. This is truly a majestic building and one of the only ancient structures left in Rome that is still intact and in use today. The only light that enters the circular building is through a hole in the center of the coffered dome called the "oculus". It is the same as in Nero's "Golden House". The building was constructed from a new material of the time called concrete, which was born after the great fire of Rome in 64 and new fireproofing codes had been enacted. The beautiful marble inlaid floor (which is of the original Roman design) is sloped slightly so that rainwater would be able to drain from inside the building. In 735, Pope Gregory III had the roof done in lead and, in 663, Emporer Constans II removed the gilded tiles from the roof. To support the heavy dome, the walls are 19 feet thick. The Rotonda's height and width are the same - 140 feet. The original portico built by M. Agrippa remain and is built on the foundation of the original temple. There were twin bell towers added on each side of the portico, but due to ridicule they were removed in 1883 leaving the original structure. The interior walls are lined with tombs, including that of painter Raphael and King Vittorio Emanuele II. It is interesting to note that when the papal seat was located in Avignon between 1305-1377, the Pantheon was used as a poultry market and fortress. In 1632, Urban VIII had the bronze from the portico/dome melted down to provide Bernini the bronze with which to build the baldacchino in St. Peter's Basilica.