The remains of the fortress can be visited
FortressCherven Bryag (Червен бряг)
Cherven (Червен) Fortress
The Cherven Fortress, whose name means "red," was a center for military, administration, economy, and culture in the Second Bulgarian Empire between the 12th and 14th centuries. Its ruins are located near the village of the same name in northeastern Bulgaria.
History+
The origins of the fortress date back to a Byzantine fortification from the 6th century, with the region already inhabited since the time of the Thracians. The first mentions of Cherven appear in an Old Bulgarian apocryphal chronicle from the 11th century. After 1235, the site gained importance when it became the seat of the medieval Bulgarian Orthodox Bishopric of Cherven. The fortress was attacked by the Mongol Golden Horde in 1242 and briefly conquered by Byzantine troops during the reign of Tsar Ivailo (1278–1280).
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://en.wikipedia.org/wiki/File:Tsjerven_%28festning%29.JPG
This description draws on the facts documented in the linked Wikipedia article; Wikipedia content is licensed under CC BY-SA 4.0. Wording and editing: Mobile History.
Location: 43.6221, 26.0201