The construction of the medieval castle of Sedan started in 1424, under Évrard II de La Marck, lord of the city. During the Middle Ages, the strength of a stronghold partly depended on the width of its walls. Those of Sedan castle are 22 to 88.5 ft wide (7 to 27 m). The fortress was therefore deemed to be impregnable as it was resistant to cannonballs and other projectiles. At that time, Sedan constituted a principality of 21 villages whose inhabitants could seek refuge in the castle in the event of an attack. The medieval fortress of Sedan, sometimes considered the largest in Europe, lives up to its motto: Undique Robur, strength everywhere in Latin.