 Considering the age and location of the Golubac Fortress , it is both large and well @-@ preserved . Its placement at the head of the Iron Gate gorge allowed for easy control of river traffic . It was the last military outpost on that stretch of the Danube river , which caused it to frequently be part of the final line of defense between Hungary and the Ottoman Empire , especially during the periods when Serbia was Ottoman @-@ held . The importance of the fortress is further indicated by the attention it received from Sigismund and Murad II , rather than just fighting between locals and commanders of nearby cities . The Golubac Fortress was declared a Monument of Culture of Exceptional Importance in 1979 , and it is protected by the Republic of Serbia . 
