Osowiec Fortress is a 19th-century fortress built by the Russian Empire, located in what is now north-eastern Poland. It saw heavy fighting during World War I when it was defended for several months by its Russian garrison against German attacks.

The Attack of the Dead Men, or the Battle of Osowiec Fortress, was a battle of World War I that took place at Osowiec Fortress, on August 6, 1915. The incident got its name from the bloodied, zombie-like appearance of the Russian combatants after they were bombarded with a mixture of poison gases, chlorine and bromine by the Germans. While coughing up blood, the Russians covered their faces with cloths and managed to rout German forces.