Simplify the following text for a Grade 9 native English-speaking person.
Original: Montreuil or Montreuil-sur-Mer is a sub-prefecture in the Pas-de-Calais department in northern France .
Simplified: Montreuil-sur-Mer ( officially , Montreuil ) is a commune . It is found in the region Nord-Pas-de-Calais in the Pas-de-Calais department in the north of France .