The Temple of Hercules Victor ('Hercules the Winner') (Italian: Tempio di Ercole Vincitore) or Hercules Olivarius is a Roman temple in Piazza Bocca della Verità, in the area of the Forum Boarium close to the Tiber in Rome, Italy. It is a tholos - a round temple of Greek 'peripteral' design completely encircled 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 (or perhaps due to) 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 marble building in Rome. The Hercules Temple of Victor is also the only surviving sacred temple in ancient Rome. Today it remains unsolved who this temple was dedicated for and for what purpose.
Dating from the later 2nd century BC, and perhaps erected by L. Mummius Achaicus, conqueror of the Achaeans and destroyer of Corinth, the temple is 14.8 m in diameter and consists of a circular cella within a concentric ring of twenty Corinthian columns 10.66 m tall, resting on a tuff foundation. These elements supported an architrave and roof, which have disappeared. The original wall of the cella, built of travertine and marble blocks, and nineteen of the originally twenty columns remain but the current tile roof was added later. Palladio's published reconstruction suggested a dome, though this was apparently erroneous. The temple is the earliest surviving marble building in Rome. The temples original dedication is dated back to circa 143-132 BCE, a time when intense construction was taking place in Portus Tiberinus.
Its major literary sources are two almost identical passages, one in Servius' commentary on the Aeneid (viii.363) and the other in Macrobius' Saturnalia. Though Servius mentions that aedes duae sunt, "there are two sacred temples", the earliest Roman calendars mention but one festival, on 13 August, to Hercules Victor and Hercules Invictus interchangeably.
In the 1st century CE the temple was hit with some sort of disaster as 10 columns were replaced with Luna marble, which is similar to the original but not an exact replica. By 1132 the temple had been converted to a church, known as Santo Stefano alle Carozze (St. Stephen 'of the carriages'). In 1140, Innocent III converted the temple into a Christian church dedicating it to Stan Stefano. Additional restorations (and a fresco over the altar) were made in 1475. A plaque in the floor was dedicated by Sixtus IV.In the 12th century CE the cella wall was replaced with brick faced concrete and windows were added as well. In the 17th century the church was rededicated to Santa Maria del Sole ("St. Mary of the Sun").The temple and the Temple of Vesta in Tivoli were an inspiration for Bramante's Tempietto and other High Renaissance churches of centralized plan. Between 1809 and 1810 CE, the surrounding ground level was lowered and the temple was restored once again. The temple was recognized officially as an ancient monument in 1935 and restored in 1996.