Factual error: The Forum shown in the film is smaller than in real life. Also, Cleopatra is shown passing through the Arch of Constantine, a monument that was built centuries after her death.
Factual error: All of the PT boats in this film are painted in the same Navy Gray used by larger warships of the US Navy in WWII. However, the real PT 109 and the other PTs in its squadron were painted green in order to better blend into their daytime anchorages or moorings near island jungles. The common green color scheme of this period was designated as "Design 5P" and incorporated Navy Green over a base coat of Ocean Green.