Montreuil-sur-Mer, Montreuil-on-the-Sea, is a subprefecture in the Pas-de-Calais Department in northern France. Though commonly called by t…Montreuil-sur-Mer, Montreuil-on-the-Sea, is a subprefecture in the Pas-de-Calais Department in northern France. Though commonly called by this name since at least the twelfth century, it was legally known as Montreuil until 31 December 2022. It is located on the Canche river, not far from Étaples. The sea, however, is now some distance away. Montreuil-sur-Mer station has rail connections to Arras and Étaples.