Battle of Eylau
After the Battle of Eylau in February 1807 French troops gathered in Osterode, from February to April 1807 Napoleon I used the castle as his headquarter. In June 1807 Polish troops of General Józef Zajączek were stationed in the town. In 1818 it became the seat of a "Kreis" (district) within the Kingdom of Prussia. In 1871 Osterode was included in the newly formed German Empire.