Osowiec Fortress (Polish Twierdza Osowiec) - Is a 19th-century fortress located in north-eastern Poland, originally built by the Russian Empire. The Russian name is Крепость Осовец i.e., Krepost Osovets. In English sources it is variously given as Osowiec, Osovets, Ossovetz, Osovetz and Ossovets. It saw heavy fighting during World War I when it was obstinately defended for several months by its Russian garrison against German attacks.