Factual error: Merlin says they threw potatoes at him. Potatoes were only in Europe from the 16th century on.
Merlin (2008)
1 factual error in season 1 - chronological order
Starring: John Hurt, Richard Wilson, Colin Morgan, Bradley James
Continuity mistake: All the castle windows on the outside of the castle are small squares yet from inside the rooms they're arched.