In the centre of Sedan Castle’s upper courtyard, the remains of the St Martin’s Church, built in the 11th century by the monks of the Mouzon Abbey, are still clearly visible. In the 13th century, the monks extended the church and built a priory around it. The new lord of Sedan, Evrard II de La Marck, drove out the monks to build his castle and included the priory in the fortified perimeter. Having become a castle chapel, the church was razed to the ground between 1822 and 1825 and replaced by a cannonball park. The castle was then only a military citadel managed by the French army.