“Hisarlaka” Fortress

Bulgaria, Bulgaria

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Hisarlaka Fortress is a well-preserved ancient and medieval stronghold perched on a hill 2 km southeast of Kyustendil in southwestern Bulgaria.

Built by the Romans around 400 AD during late antiquity, the irregular polygonal structure spans 117 by 175 meters with massive 10-meter-high walls up to 3 meters thick and about 14 towers of varying shapes—round, rectangular, and irregular—plus two main gates and five secret passages.

Destroyed multiple times by Huns, Avars and Slavs around 598-599 AD, and finally Ottoman forces in the 15th century, it served as a key Bulgarian Empire defensive site after repairs under Justinian I and during both the First and Second Bulgarian Empires.