In the hyperinflation of 1923, the firm printed Kruppmarks for use in Essen, which was the only stable currency there. France and Belgium occupied the Ruhr and established martial law. French soldiers inspecting Krupp's factory in Essen were cornered by workers in a garage, opened fire with a machine gun, and killed thirteen. This incident spurred reprisal killings and sabotage across the Rhineland, and when Krupp held a large, public funeral for the workers, he was fined and jailed by the French. This made him a national hero, and he was granted an amnesty by the French after seven months.