In 1480, the castle of Haut-Koenigsbourg was modernized and adapted to the latest military techniques by the Thiersten family. In front of the keep, a double wall belt flanked by towers was equipped for shooting firearms. A bastion was also added on the mountainside. The rooms of the castle were vaulted to prevent fires. The Thiersteins finally set up a mill, a forge, and stables. Thus, crowning the entire summit of the mountain, the Koenigsbourg became the most important castle in the province.