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.
Revealing mistake: When Caesar's ship arrives in the Alexandria marketplace, he tells his men to "go marketing" rather than force their way through the crowd with swords. Rufio says "you're not serious?" He then silently mouths along with Caesar's reply, "We shall shop our way to the palace steps." (00:11:30)