The original castle of Lord Evrard II de La Marck was built from 1424 around an older Benedictine priory. The small independent principality of Sedan – twenty-one villages in all – was not recognised until the middle of the 16th century, but Evrard’s descendants enlarged and strengthened the castle over the years. A princely dwelling was built during the Renaissance, the walls were extended (up to 27 metres thick) and four huge bastions were added. The largest medieval fortress in Europe was deemed impregnable. In 1642, the principality and its fortress were ceded to the France of King Louis XIII.