Completed the following sentence: 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.<unk> There was a dense network of castles which guarded the trade routes and the strategic heights.<unk> The largest and most important castles include Lyutitsa, Ustra, Tsepina, Mezek, Asenova krepost and many others. ️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️
Bulgarian<unk> Ottoman wars.