Komárno fortification system

Komárno - Komárom fortification system is a system of forts, bastions, and fortifications in and around the towns of Komárno and Komárom on the banks of both the Danube and Váh rivers. The fortification system of town Komárno is the biggest fortification in Slovakia, and as a whole complex with fortifications on the Hungarian side of the Danube it is the biggest fortification in former Austro-Hungarian Empire.

Source: Wikipedia