The Walls of Dubrovnik (Croatian: Dubrovačke gradske zidine) are a series of defensive stone walls surrounding the city of Dubrovnik in southern Croatia. With numerous additions and modifications throughout their history, they have been considered to be amongst the great fortification systems of the Middle Ages, as they were never breached by a hostile army during this time period. In 1979, the old city of Dubrovnik, which includes a substantial portion of the old walls of Dubrovnik, joined the UNESCO list of World Heritage Sites.The oldest systems of fortifications around the town were likely wooden palisades. Today's intact city walls, constructed mainly during the 12th–17th centuries, mostly a double line, have long been a source of pride for Dubrovnik. The walls run an uninterrupted course of approximately 1,940 metres (6,360 ft) in length, encircling most of the old city, and reach a maximum height of about 25 metres (82 ft). The bulk of the existing walls and fortifications were constructed during the 14th and 15th centuries, but were continually extended and strengthened up until the 17th century.This complex structure, amongst the largest and most complete in Europe, protected the freedom and safety of the "civilised" and "sophisticated" Republic of Ragusa that flourished in peace and prosperity for some five centuries. The walls were reinforced by three circular and 14 quadrangular towers, five bastions (bulwarks), two angular fortifications and the large St. John's Fortress. Land walls were additionally reinforced by one larger bastion and nine smaller semicircular ones, like the casemate Fort Bokar, the oldest preserved fort of that kind in Europe. The moat that ran around the outside section of the city walls, which were armed by more than 120 cannons, provided superb city defense capabilities.