Temple of Hercules Victor

The Temple of Hercules Victor or Hercules Olivarius is a Roman temple in Piazza Bocca della Verità, the former Forum Boarium, in Rome, Italy. It is a tholos, a round temple of Greek 'peripteral' design completely surrounded by a colonnade. This layout caused it to be mistaken for a temple of Vesta until it was correctly identified by Napoleon's Prefect of Rome, Camille de Tournon.

Despite the Forum Boarium's role as the cattle market for ancient Rome, the Temple of Hercules is the subject of a folk belief claiming that neither flies nor dogs will enter the holy place. The temple is the earliest surviving mostly intact marble building in Rome and the only surviving one made of Greek marble.

Source: Wikipedia