Factual error: The 13th legion's symbol was a lion, not a boar as depicted in the series.

Factual error: Vercingetorix was indeed displayed publicly in Caesar's triumph, but he was executed afterwards, not during the triumph itself.

Factual error: Brutus proposes that Caesar be made imperator. The word imperator would come to mean emperor during the age of the Roman Empire, but it did not have that meaning during Caesar's time. Imperator was a military title which Caesar had been given long before the events in this episode. Even if the word is used with its current meaning it's an error, as Caesar never became an emperor. The word Brutus would have used is dictator.