It then runs for about 560 kilometres (350 mi), first in a south-easterly direction along the border, then eastward across Bulgaria, forming a natural barrier between the northern and southern halves of the country, before finally reaching the Black Sea at Cape Emine.

In much of the central and eastern sections, the summit forms the watershed between the drainage basins of the Black Sea and the Aegean.

A prominent gap in the mountains is formed by the predominantly narrow Iskar Gorge, a few miles north of the Bulgarian capital, Sofia.

Most of Europe's large mammals inhabit the area including the brown bear, wolf, boar, chamois and deer.

the name was brought to the region in the 7th century by Bulgars[citation needed] who applied it to the area, as a part of the First Bulgarian Empire.

[citation needed] In Bulgarian, the archaic word balkan (балкан) was borrowed from Turkic and means "mountain".

[8] Other names used to refer to the mountains in different time periods include Aemon, Haemimons, Hem, Emus, the Slavonic Matorni gori and the Turkish Kocabalkan.

The area of the Stara Planina has always been sparsely populated and inaccessible because of the rugged and forested terrain, but also as a location of the Serbian-Bulgarian border.

It was a natural fortress of the Bulgarian Empire for centuries and formed an effective barrier to Moesia where most of the medieval capitals were located.

In the battle of the Varbitsa Pass, Khan Krum decisively defeated an enormous Byzantine army, killing Emperor Nikephoros I.

Also close to Botev is Shipka Pass, the scene of the four battles in the Russo-Turkish War, 1877-78, which ended Turkish rule in the Balkans.

[22] Due to the park's high altitude, the ichthyofauna consists of six fish species, with brown trout being the dominant one.

[23] Vrachanski Balkan Nature Park is situated in the western section of the mountain range and spans an area of 301.29 km2.

[35] Since the early XXI century there have been several records of the Eurasian lynx, which has been considered extincts in Bulgaria since the 1940s, in a number of localities along the Balkan Mountains.

Nature park Stara Planina was established in 1997 and since 2009 is in its present borders, covering an area of 1,143.22 km2 (441.40 sq mi).

[40] Montane ecosystems are diverse and include several plant communities: forests, shrubs, meadows, pastures and peatlands.

Other plants include shrub alder, steppe pedunculate oak, but also rare and endangered species like European pasqueflower, yellow pheasant's eye, Kosovo peony, common sundew, Heldreich's maple, martagon lily, pygmy iris and marsh orchid.

[40] In total, there are 1,190 plant species, including a locally endemic winged bellflower (Campanula calyciliata) and Pančić's frog grass (Senecio pancicii), which can be found only on the mountain.

In 2022, several independent surveys from various universities and institutes were conducted, in order to list all of them, to enhance their protection, and to check possibilities for potential plantation production.

Over 30 mammalian species are found in the park, including lesser mole-rat, hazel dormouse and the Tertiary relict, European snow vole.

[46] Human heritage spans from the prehistoric remains, Classical antiquity including the Roman period and late mediaeval monastic complexes.

There are numerous examples of the ethnic edifices characteristic for the architecture of the region in the late 19th and early 20th century (houses, barns, etc.

)[40] Serbian section of the mountain is seen as a location for dozens of micro hydros, mini power plants which caused problem with the environmentalists and local population.

In order to prevent further degradation, the Nature Park Stara Planina was nominated for the UNESCO's Man and the Biosphere Programme and for the world list of geoparks, while over tens of thousands of citizens signed petitions against the micro hydros and numerous protests have been organized by the local population.

The activism resulted in various physical altercation between the local citizens on one, and contractors and their security guards on the other side, amidst the police interventions.

[52] In September 2019, Pirot city administration announced it is removing from the spatial plan all 43 existing locations for the micro hydros on the protected area of Stara Planina.