Jupiter's Darling (1955)
Jupiter's Darling is a musical romance film released by MGM in 1955 and directed by George Sidney. It starred Esther Williams as the Roman woman Amytis, Howard Keel as Hannibal, the Carthaginian military commander and George Sanders as Fabius Maximus, Amytis's fiance. In the film, Amytis helps Hannibal swim the Tiber River to take a closer look at Rome's fortifications.
More at Wikipedia.