Ustra Fortress

Ustra is a fortress in the Rhodope Mountains and one of the best preserved in the region. With the foundations of many buildings and towers surviving, it is an intriguing archaeological site. Built in the Middle Ages, Ustra was predominantly under Byzantine rule.
The fortress was built in the tenth century to protect the trade route passing through the area. Near the village of Ustren in Dzhebel Municipality, Kardzhali Province, it stands on a steep summit offering extensive views.
Archaeological evidence links Ustra's early dating to the reign of Constantine VII Porphyrogenitus, 913–959. During this period the Bulgarian tsar Simeon I probably captured the fortress, but later returned it to Byzantium and became "basileopator", the Byzantine emperor's senior guardian, by marrying one of his daughters. After the emperor's mother Zoe repudiated the treaty in 917, the ensuing Battle of Achelous that year brought a crushing Byzantine defeat. Nevertheless, following Simeon's death in 927, Ustra remained permanently under Byzantine rule. Even so, during the period of mature feudalism and the Second Bulgarian Empire, in the twelfth–fourteenth century, there is indirect evidence that Ivan Asen II captured the fortress.