The remains of the circular structure of the Serapeum, a covered market place constructed during the reign of the Flavian emperors, The Serapeum and the town of Pozzuoli are built on the Phlegrean Fields volcanic complex which inflates with magma and then deflates, thus rising and falling. The site and its geology was studied in the 1830's by the geologist Charles Lyell and has been a symbol of uniformitarianism. Italy. Roman.