Assault on Friedrichstadt Day is observed in Denmark every October 4, commemorating the anniversary of the last major battle of the First Schleswig War, which took place on this date in 1850. The conflict was fought between Denmark and the German Confederation over the control of the duchies of Schleswig and Holstein, which were under Danish rule but had a pro-German sentiment among many residents. On October 4, Danish forces, despite being outnumbered, successfully repelled an assault by Schleswig-Holstein troops on the town of Friedrichstadt, although the defense resulted in significant destruction, including the burning of the town hall and a 17th-century church. This day is recognized as a flag-flying day in Denmark, celebrating a significant military victory in the nation's history, even though Denmark ultimately lost the duchies in 1864. The observance reflects on Denmark's military heritage and the historical significance of the battle.