From 1462, the Thierstein family began work on the Haut-Koenigsbourg castle. The brothers Oswald and Guillaume are in charge of rebuilding the fortress. It results in a modernized castle, enlarged and adapted to the latest military techniques. At the front of the keep, to the south, a double belt of walls flanked by towers is equipped for using firearms. A star bastion now stands on the mountain-facing ramparts. Nonetheless, the castle is besieged for 52 days in 1633 and falls into the hands of the army of Sweden.