The caves and potholes of Serbia have been studied for more than 100 years and to date more than 4000 locations have been explored.  Inflow, outflow and through-caves are predominant and the length of the largest caves ranges from 2 to 7.5 km. Because of the relatively thin limestone mass, potholes are fewer in number than caves. Both corrosive (karst) and ponor (active) cave types are equally represented in the group of the deepest locations. The depth of the largest caves ranges from 150 to 280 m.