The Temple of Hercules Victor is a small Roman temple located in the area of the Forum Boarium, along the Tiber river. This curious structure immediately catches the eye and is known as a tholos, a round Greek temple encircled by a colonnade.

The temple was constructed around the year 120 BC, making it the oldest still-standing marble building in Rome, and the second oldest building in the city. It's also the only surviving structure in Rome made out of the prestigious Greek marble. The temple was dedicated to Hercules, described by the epithet of Victor ("Winner"), but it's also known as the Temple of Hercules Olivarius, the protector of oil.

Over the centuries, some parts of the temple, like the roof, were replaced after being damaged. The structure was transformed into a church in 1132 and dedicated to Saint Stephen, patron saint of carriages. It was later rededicated to Saint Mary of the Sun.

Eventually, the structure was returned to its original state as a Roman temple during the early 20th-century. An old folk tale claims that neither dogs nor flies can enter this temple.