The main altar of the Pantheon in Rome. Originally constructed in 27 B.C., the Pantheon was rebuilt by the Emperor Hadrian in A.D. 126; it became a Roman Catholic church in the 7th century. The tombs of Raphael, two Italian kings, and various other notables are located in the Pantheon. It is considered one of the best preserved of all Roman buildings. Its dome, 43.3 m (142 ft) wide and constructed of unreinforced concrete, sets it apart from other structures of the time.