When Talus is cornered by Cobra's army outside the city walls, he looks back to see Mathayus coming through the smoke after the explosion. Mathayus has soot smudges on his face and arms. The shot goes back to Talus and again to Mathayus. This time, Mathayus is clean.
During the fight between Silda and Tsukai, Silda starts the fight using two swords but changes to a single sword mid-fight, then back to using two swords. Throughout the sequence,Silda does not appear to drop or pick up the sword, nor is there enough time to perform that action.
Mathayus is outside of Talus' camp when he uses his telescope and you see his scar on the opposite arm, all other times it's on the right arm.
Mathayus and Olaf are woken by five tigers intruding on their camp. Tigers are solitary by nature, and seeing five together in the wild is highly unlikely.
Although set in primitive times some 5,000 years ago, the women have shaved legs and armpits.
Talus' army uses counterpoise trebuchets. The big sling shot weapons with the counter weight. This particular type was not invented until the middle ages around the 11th century. If we follow the time line of the other movies that places them about 4000 years before they were invented.
During the wide-shot of the palace after the death of Ramusan, there is a security/surveillance camera visible attached to the wall pointed down at the entrance to the palace.
Historically, ninja date to the 15th century CE, not the 31st BCE.
Talus and Mathayus both use telescopes. Mathayus uses a crystal that he moves to focus. Talus has a glass lens telescope which was not invented until around 1608. This is about 2500 years after the movie is supposed to take place.
When the army of Callus is preparing for battle they have an array of battle flags. There appear to be the flags of Scotland and England as well as one with a French fleur-de-lis on it.