Consecrated in 609 as an ancient Roman temple reconsecrated to St. Mary and the Martyrs — explicitly, its founders said, so that veneration would take place ‘where not gods but demons were formerly worshipped’ — the Pantheon remains an active parish church, not only a monument, though few visitors realize it. Each Pentecost, red rose petals are dropped through the oculus after Mass, traditionally by Rome’s firefighters from the roof.