In the Middle Ages the mountain was part of the Bulgarian and Byzantine Empires and often changed hands between the two countries. There was a dense network of castles which guarded the trade routes and the strategic heights. The largest and most important castles include Lyutitsa, Ustra, Tsepina, Mezek, Asenova krepost and many others. Between 1371 and 1375 the Rhodopes fell under Ottoman occupation in the course of the Bulgarian–Ottoman wars.