Ston city walls consist of the main wall and three forts (Veliki Kaštio, Koruna, and Podzvizd), forty-one towers, seven bastions, (Sokolić, Arcimon in Ston, the three bastions of Veliki Kaštel, the Podzvizda bastion and the Arcimon in Mali Ston), four pre-walls (the eastern and south-western Ston pre-walls, the Mali Ston pre-wall and the Korun pre-wall), and a water-filled moat that stretches around the western, southern and eastern edges of Ston. The construction of these magnificent walls began in the early 16th century. Originally 7000-meters long (22 965 ft.), they consist of several parts; the Stone city walls, the Mali Ston city walls, and the Big wall with its three forts. It took almost four centuries to finish these complex defense walls, as the builders had to adapt to the rough terrain and advancements in warfare technology. The walls were last used for defense in the 19th century, and today they are a priceless monument of immense architectural and cultural value. Entrance fee is 10 EUR for Adults and 5 EUR for kids.