The Balkan Mountains are the largest Bulgarian mountain range in terms of area and gave their name to the entire Balkan Peninsula. The range was known earlier as Haimon, Haimos, and Haemus (of Thracian origin) which mean watershed, border. It spreads out from the Timok River (the border with Serbia) in the west to the Black Sea in the east. The average height above sea level of the central chain is 722 m (2345 ft). It is the largest in area, around 25,000 km2 (9600 miles2) together with its foothills, and third in height – after Rila and Pirin – in all of Bulgaria. Despite its Bulgarian name Stara Planina – Old Mountain in Bulgarian, it is a young formation. It consists of granite and smaller amounts of limstones, gneiss and shales. A portion of the relief is typically alpine. The Balkan Mountains are a climactic divider between the borderline continental climate of northern Bulgaria and the milder climate of southern Bulgaria with its Aegean influence. Fogs and strong winds, which can cause landslides, are characteristic of the Balkan Range.
The range is divided into three main sections: western, central and eastern.