When Gordian is lying on the ground in the arena and Marcus is above him with his sword waiting for the Emperor's decision if Gordian is to live or die, Gordian is first shown with his shirt lifted up completely bare-chested. The next scene, he is totally covered by his shirt.
The goof item below may give away important plot points.
In the opening scene, the Cyclops is attacked with stake with a point at one end. Although the stake never leaves the attacker's hands, it somehow reverses so that the point stabs the attacker when the Cyclops pushes it.