Fortifications

Osowiec-Twierdza

A tsarist fortress built in the second half of the 19th century in the Biebrza marshes, designed according to the Russian school of fortification with a fully developed polygonal system. In the early 20th century it ranked among the most modern fortresses in the world. It went down in history for its heroic defence in the First World War — and was never captured.

The “Attack of the Dead Men”

Osowiec earned its fame during a 6.5-month defence in 1914–1915. The legend was born in 1915, when German forces shelled the garrison with gas — yet the counterattacking Russian soldiers, poisoned by the chemical agents themselves, drove the attackers back. The episode became known as the “Attack of the Dead Men” and remains one of the most famous First World War stories on Polish soil.

A fortress in the marshes

The fortress is surrounded by the marshes of the Biebrza valley, which were themselves part of its defences. The area is now under nature protection, and a museum documenting the history of the garrison operates in the former military facility. A trail through the marshes runs along the embankments and causeways.

Practical notes

Combine your visit with the area's nature paths — sturdy boots are essential as the ground can be waterlogged. Allow 1–2 hours for the fortress and museum, half a day for the marsh trails. Spring and early summer are the most rewarding seasons.