Ustra
In short
A medieval fortress located in the eastern Rhodope Mountains of southern Bulgaria. It stands as one of the highest and best-preserved fortifications in the mountain range.
In plain words
Ustra is an old stone castle built high up in the mountains. It was used by different empires, including the Byzantines and Bulgarians, to guard the area before the Ottoman Turks arrived.
A simple example
Archaeologists visit the site to study the ancient stone walls and how people lived in the mountains during the Middle Ages.
Why it matters
It provides vital historical evidence of how different empires fought for control over the Rhodope region. Its high position shows how important mountain defence was in medieval warfare.
Easy to mix up
Do not confuse it with Ustrem, which is a different location in Bulgaria.