Ruins Krivus located in the southern Rhodope Mountains, in the district of Kardzhali, near the village of Bashev. They are located on a rocky promontory a hundred meters above the level of the Arda River, surrounding three sides of the ancient fortress.

Historians believe that the medieval Bulgarian fortress Krivus was built in the 10th century. The location was not chosen by chance - the castle was difficult to obtain due to the surrounding steep cliffs. The main function of a fortress and Krivus located near the fortress Patmos was the defense area around the Arda River in the eastern part of the Rhodope Mountains. Finally, the citadel was destroyed, like most Bulgarian fortifications, during the Ottoman invasion. In the history preserved mention of the fact that in the era of Ottoman rule the fortress was used as a women's prison.

Have survived and are in good condition fortress wall, which has a thickness of about 2.5 meters at the base and 1.75 above, and in the height of about five meters, defensive towers and two well-fortified entrance to the fortress. It is also perfectly preserved citadel - inside the fortress - the size of 40 by 50 meters and its surrounding battlement, six meters in height. In the center of the court was erected a small church, but from her left only ruins. Between the river and the fortress it was laid under the ground a special tunnel, which links to the territory of a fortified defensive structure with water. It was created in the event of siege by enemies and is a unique example of engineering of the era. Today the tunnel is filled and difficult to find.

In the excavations of the ancient fortress Krivus found many ancient coins, jewelry, and Christian symbols, such as stone crosses, and weapons. The fortress was repeatedly mentioned in Byzantine chronicles George Akropolita. Today the ruins are open to visitors. From the top of a hill with views.