Complex sentence: They are also said to have removed the great doors to the Abbey so that such a mistake could not occur again, so if someone said "do you come from Bardney?", it meant that you had left the door open.
Split into simpler sentences: They are also said to have removed the great doors to the Abbey so that such a mistake could not occur again. So if someone said "do you come from Bardney?", it meant that you had left the door open.