The New Georgenburg Fortress, located in the Polish village of Modlin, is situated 30 km northwest of Warsaw, at the confluence of the Vistula and Narew rivers. It is one of the largest preserved defensive structures in Poland and the longest fortress in Europe, with barracks measuring 2250 meters in length.

Due to its location at the confluence of rivers, Modlin has excellent defensive characteristics. These advantages were recognized by Swedish King Charles Gustav, under whom the construction of the first fortifications began. Later, during the Northern War, the work was continued by Saxon Field Marshal Adam von Steinau. In 1794, Russian General Pyotr Suhtelen proposed a project for a new fortress, but construction did not commence.

The modern fortress was commissioned by Napoleon in December 1806. More than 10,000 peasants participated in the construction based on the design by engineer François Chasseloup-Laubat. After the French left, the fortress was occupied by the troops of the Duchy of Warsaw under the command of Hermann Dandels. After the 1830 uprising, the fortress was fortified by order of the Russian emperor to protect the western borders of Russia and prevent possible uprisings. In 1834, the fortress was named New Georgenburg, and the fortification works were led by General Ivan Den. At the end of the 19th century, circular barracks for 20,000 soldiers were built, extending 2250 meters.

During World War I, the fortress was subjected to attacks by German troops, aerial bombardments, and was captured in August 1915. In World War II, it again defended against the German army under the command of General Viktor Tome.

Today, many fortifications are abandoned and losing their original features; however, some buildings are successfully used for tourism purposes. In October 2008, the fortress was included in the register of monuments of Mazovia. Currently, tours are conducted where visitors can see the barracks, part of the fortifications, and forts. Historical battle reenactments take place at the fortress annually.