Nysa Stronghold from the very beginning, the city had wooden fortifications surrounded by a moat. In the mid-fourteenth century, Nysa received huge medieval walls with four gates and 28 towers. The reconstruction of the fortifications begins in 1643, the town receives a system of 10 bastions, a water moat and a hidden road between the moats. The situation changes after the entry of Prussian troops led by King Frederick II. The fortification of the city begins, which was to defend the newly created Prussian-Austrian border. Nysa becomes a garrison town and a modern fortress. They are built, among others forts, redoubts, the garrison district "Friedrichstadtt" is established. The development of the fortress takes over 100 years until it loses its charter in 1903. It defended itself long and effectively against the Habsburg troops during the Second Silesian War, and repelled the attack of Napoleon's troops for 114 days. In its history, it was also a great POW camp, where famous French were kept: Marie Joseph, Marquis de la Fayette and Charles de Gaulle. Today, the fortress becomes one of the most important attractions of Nysa and the Opole Voivodeship.
Since 2000, the Nysa fortress festival has been organized in Nysa Fortress Days. Every year, reconstructors of the Prussian-Napoleonic era come to the city from all over Europe to take part in the reconstruction of the Battle of Neisse in 1807, which is the culmination of this event. The battle of 1807 was one of the most important military episodes of the city. During the 114-day siege, Nysa fell into ruins and the city was captured by the troops of the Napoleonic coalition.