The largest medieval castle in Europe overlooks the town of Sedan and the Meuse river with its 35,000 m2. The story begins in 1424, when Evrard II de La Marck, a Rhineland lord, acquired the Sedan seigneury. He decided to build his castle on the site of the Saint-Martin priory. He drove out the monks and integrated the former priory into the castle’s walls. The church of Saint Martin became the castle chapel. The square tower, which had previously been the monks’ living quarters, was transformed into a keep. The entrance to the castle was defended by two twin towers protected by a small castle gate.