Brutus is shown as being killed by the soldiers of Octavius. In fact, he committed suicide.
The hands of Cicero were in fact not nailed to the doors of the Senate house but to the 'rostra', the speaker's scaffold on the Forum.
In the beginning of the Battle of Philipi, a banner belonging to the "XXVII" (27th) Legion is shown during Brutus and Cassius attack against Octavian and Anthony's lines.
In reality there never was a "XXVII" (27th) Legion at any point in ancient Roman history.
When Titus Pullo kills Cicero, you can clearly see the length of the sword is alot smaller when he pulls the sword out from his shoulder.