Panteón de Agripa
Some remains of many Roman temples still survive, above all in Rome itself, but the relatively few near-complete examples were nearly all converted into Christian churches (and sometimes subsequently to mosques), usually a considerable time after the initial triumph of Christianity under Constantine. The decline of Roman religion was relatively slow, and the temples themselves were not appropriated by the government until a decree of the Emperor Honorius in 415. Santi Cosma e Damiano, in the Roman Forum, originally the Temple of Romulus, was not dedicated as a church until 527. The best known is the Pantheon, Rome, which, however, is highly untypical, being a very large circular temple with a magnificent concrete roof, behind a conventional portico front.