The role of the Haemus Mountains (that is Stara Planina and Sredna Gora) as a geographical factor is visible in the fact that between the close of the 7th century and the beginning of the 9th century, the eastern parts of that massif turned naturally into a political border between Bulgaria and Byzantium. Although in later times this border moved further to the south, even for longer periods, still the mountain ridge remained the most lasting demarcation element in the Byzantine-Bulgarian relations and the most certain determinant of the heart of the Bulgarian statehood (the so-called internal area of Bulgaria), which was concentrated in the years 680/681-971, i.e. excluding the period of the reign of the Komitopouloi, in the area between the mountains and the Danube valley. If the Haemus was the political border of Bulgaria for almost a half of the functioning of this state during the period of 7th-11th c., it proves irrefutably that the massif was of great significance for the political history of Bulgaria and its contacts with Byzantium.
