Some concrete bunkers were built before the Second World War by the army of the kingdom. Type MG / 12 (machine gun nest) in the area of Petrovaradin Fortress.

Bunker MG/12 in Hornwerk (Petrovaradin fortress - south-west side) (photo: Nenad Šeguljev 2004)

Bunker MG/12 in Wasserstadt (north side of Petrovaradin fortress) (photo: Miroslav Farkaš 2014)