What Roman temple in Rome, built in the 2nd century BC, is the oldest surviving marble temple?

The Roman temple in Rome built in the 2nd century BC and recognized as the oldest surviving marble temple is the Temple of Hercules Victor.

The round temple stands in the former Forum Boarium, Rome’s ancient cattle market, near the Tiber. It is generally dated to about 143–132 BC, though scholars debate its precise construction date and patron. The building is a tholos: a circular cella surrounded by a ring of Corinthian columns.

The temple is often confused with the nearby Temple of Vesta because both are circular. That identification was corrected in the modern period, and the monument is now associated with Hercules Victor, also called Hercules Olivarius. Nineteen of its original twenty columns survive, and its preservation was helped by its conversion into a Christian church in the Middle Ages. It is more precisely described as Rome’s earliest surviving mostly intact marble building, rather than the oldest marble structure of any kind anywhere.