Built in late 19th c., the stronghold was the core element the fortification complex guarding the western borders of the Russian Empire. Originally built of bricks and stone, the stronghold was reinforced with concrete during modernisation works held at the beginning of 20th c. During World War I, in 1915, the fortress stood three German sieges including a battle gas attack, which gained it a reputation similar to that of the Battle of Verdun in 1916. In 1998, the Osowiec Stronghold was put on the National Heritage Register. Nowadays, the buildings of the Central Fort house the Museum of Osowiec Stronghold. The Osowiec Fortification Society offers guided group tours of the fortress and museum.