Continuity mistake: In the scene where Caesar orders his guards to kill and seize Mel Brooks, he calls for more wine and a servant comes to pour him some If you notice his shirt, it is clean and white. In the shot right after he calls for it, when the servant is walking up behind Caesar laughing, you can see that Caesar's shirt is stained purple. This is caused from repeated takes, because right after the servant walks up he spills the entire container on Caesar. But yet, in the finished movie, Caesar's shirt is purple before it even gets spilled on.
Other mistake: After Leonardo sets up his canvas to begin painting The Last Supper with Jesus with his disciples, he says "hold it" and then the camera flips to show the men (and Comicus) now situated behind the table. Look at the disciple in the blue tunic at the right, who first looks off to his right, then corrects his position, and faces left, with his arms extended. (00:52:32)