The last king of Rome, Lucius Tarquinius Superbus, and his allies, the Latins, waged war on the infant Roman Republic.

Before the battle, the Roman dictator Aulus Postumius Albus Regillensis vowed to build a temple to the Dioscuri (Castor and Pollux) if the Republic were victorious.

During the imperial period, the temple housed the office for weights and measures, and was a depository for the State treasury.

[4] The archaic temple was completely reconstructed and enlarged in 117 BC by Lucius Caecilius Metellus Dalmaticus after his victory over the Dalmatians.

Commemorating the initial victory at Lake Regillus, a large cavalry parade was held each year on July 15 and featured as many as 5,000 young men carrying shields and spears.

[5] According to Edward Gibbon, the temple of Castor served as a secret meeting place for the Roman Senate.

The temple was possibly already falling apart in the fourth century, when a wall in front of the Lacus Juturnae was erected from reused material.

According to ancient sources, the temple had a single central stairway to access the podium, but excavations have identified two side stairs.

The temple complex was excavated and studied between 1983 and 1989 by a joint archaeological mission of the Nordic academies in Rome, led by Inge Nielsen and B.