Factual error: The Forum shown in that film is smaller than in real life. Also, Cleopatra is shown passing through the Arc of Contantine, a monument that was built centuries after her death.
Great sites
Mistakes
Cleopatra's barge shows that it has linoleum flooring. However, much marble would have sunk the barge because of its weight. See more...
Cleopatra mistakes
Factual error: The Roman legionaries are using armor and shields first used over a century later, and there are no transverse crests to mark the many centurions that would have been in each unit.
Deliberate "mistake": In order to get to Julius Caesar and evade her nasty brother Ptolemy's assassins, Cleopatra concealed herself in a rug that she has a slave carry to Caesar. Look at the furled rug the slave carries on his shoulder. Then watch Cleopatra fall out as the slave tosses the rug to the floor and unfurls it. The slave would have needed wall-to-wall carpeting to hide her.