Ustra is a castle in the eastern Rhodope Mountains

Rhodope Mountains

The Rhodopes are a mountain range in Southeastern Europe, with over 83% of its area in southern Bulgaria and the remainder in Greece. Its highest peak, Golyam Perelik , is the seventh highest Bulgarian mountain...

 in southern Bulgaria

Bulgaria

Bulgaria , officially the Republic of Bulgaria , is a parliamentary democracy within a unitary constitutional republic in Southeast Europe. The country borders Romania to the north, Serbia and Macedonia to the west, Greece and Turkey to the south, as well as the Black Sea to the east...

. Its ruins lie 4 kilometres (2.5 mi) southwest of the village of Ustren

Ustren

Ustren is a village in the Kardzhali Province, southern Bulgaria. it had 296 inhabitants.The village is situated in a mountainous area in the eastern Rhodopes 11 km to the south-west of Dzhebel. There is a school and a chitalishte...

 situated on a hill at approximately 800 metres (2,624.7 ft) above sea level.

The fortress was built in the 10th century AD to protect an important trade route. Its was taken by the armies of Simeon the Great

Simeon I of Bulgaria

Simeon I the Great ruled over Bulgaria from 893 to 927, during the First Bulgarian Empire. Simeon's successful campaigns against the Byzantines, Magyars and Serbs led Bulgaria to its greatest territorial expansion ever, making it the most powerful state in contemporary Eastern Europe...

 (893-927), but after his death, it was among the lands given back to Byzantium

Byzantine Empire

The Byzantine Empire was the Eastern Roman Empire during the periods of Late Antiquity and the Middle Ages, centred on the capital of Constantinople. Known simply as the Roman Empire or Romania to its inhabitants and neighbours, the Empire was the direct continuation of the Ancient Roman State...

 in return for recognition of the imperial title of the Bulgaria

Bulgaria

Bulgaria , officially the Republic of Bulgaria , is a parliamentary democracy within a unitary constitutional republic in Southeast Europe. The country borders Romania to the north, Serbia and Macedonia to the west, Greece and Turkey to the south, as well as the Black Sea to the east...

n rulers. Between the 12th and 14th centuries, it frequently changed hands between the two empires, but the Byzantines held it most of the time.

The ruins are located 1.5 kilometre (0.93205910497471 mi) from the road between Ustren and Zlatograd

Zlatograd

Zlatograd is a town in Smolyan Province, Southern-central Bulgaria. It is the administrative centre of the homonymous Zlatograd Municipality. As of December 2009, the town has a population of 7,110 inhabitants....

. There is a hut of the same name nearby. The height of the surviving walls is 10 metres (32.8 ft).

Namesake

Ustra Peak

Ustra Peak

Ustra Peak is a rocky peak of 195 m on the coast of Walker Bay, Livingston Island in the South Shetland Islands, Antarctica...

 on Livingston Island in the South Shetland Islands

South Shetland Islands

The South Shetland Islands are a group of Antarctic islands, lying about north of the Antarctic Peninsula, with a total area of . By the Antarctic Treaty of 1959, the Islands' sovereignty is neither recognized nor disputed by the signatories and they are free for use by any signatory for...

, Antarctica is named after the fortress.