The Battle of Lake Regillus was a legendary Roman victory over the Latin League shortly after the establishment of the Roman Republic. The Latins were led by an elderly Lucius Tarquinius Superbus, the seventh and last King of Rome, who had been expelled in 509 BC, and his son-in-law, Octavius Mamilius, the dictator of Tusculum. The battle marked the final attempt of the Tarquins to reclaim their throne. According to legend, Castor and Pollux fought on the side of the Romans.