Krivus is a medieval Bulgarian fortress that existed between the 12th and 14th centuries. It is located on a high hill with breathtaking scenery, surrounded by the Arda River. Here the river forms one of its most famous meanders.There are many steep slopes. The castle is naturally protected by the river, so to conquer it was very difficult. It is assumed that many imprisoned Bulgarian girls and women were kept inside the castle. There used to be a stone inscription.The inhabitants of the castle supplied themselves with water through an underground channel that went all the way to the river that surrounds the "Krivus"" on three sides. There are many fragments of medieval pottery. A necropolis from the same period has been found nearby.Some Byzantine sources mention the fortress. For example, the famous chronicler George Akropolit reports that in 1254, when Bulgaria was fighting with the Byzantines, they managed to conquer many towns and lands near the Maritsa River. Following their battle march, they entered into the thick forests of the Rhodope Mountain and after a brief fighting, captured the important fortresses- Stenimahos, Krichim and Tsepina. Later on, they forced their way through the defense systems of several important fortifications, whose names are referred to by Geogr Akropolit-Krivus. These fortresses were Krivus, Perperikon Ustra and Patmos. For a short time the Bulgarians conquered much of the land in the Rhodope Mountains, which had been in the hands of Byzantium.