Belgrade Fortress stands on top of a cliff overlooking the confluence of the Sava and the Danube. This is the last raised ground in the Balkan Peninsula before the vast stretch of flatland of the Pannonian Basin, extending all the way to Central Europe. The Fortress controls the access to the Pannonian Basin and the navigation on the Sava and the Danube, a position of outstanding strategic importance, accounting for its role as a border fortress throughout much of its history. It served to guard the border between the Roman Empire and barbarian lands across the Danube and the border between the Ottoman and Austro-Hungarian Empires, to name a few, which explains why it was so often destroyed, rebuilt and redesigned. The Romans were the first to build a fort at this site in the late 1st century as the HQ for the IV Roman Legion - Flavia Felix. Its remnants are barely visible today. Belgrade Fortress consists of the Upper Town, Lower (or Water) Town and Kalemegdan Park. The present layout of the Fortress took shape in the late 18th century, but there used to be many more buildings within its walls that had perished in different battles. http://www.beligrad.com/fortress.htm