Sredna Gora ( ) is a mountain range in central Bulgaria, situated south of and parallel to the Balkan Mountains and extending from the river Iskar to the west and the elbow of river Tundzha north of the city of Yambol to the east. Sredna Gora is 285 km long, reaching 50 km at its greatest width. Its highest peak is Golyam Bogdan at . It is part of the Srednogorie mountain chain system, which extends longitudinally across the most country from west to east, between the Balkan Mountains and the Sub-Balkan valleys to the north and the Kraishte, Rila and the Upper Thracian Plain to the south.
The mountain is divided into three parts by the rivers Topolnitsa and Stryama — Ihtimanska Sredna Gora to the west, Sashtinska Sredna Gora in the center, and Sarnena Sredna Gora to the east. Compared to most other mountain ranges in Bulgaria, Sredna Gora has lower average altitude, which determines higher temperatures and lower precipitation. There is an abundance of mineral springs all over Sredna Gora with many spa resorts, such as Hisarya, Starozagorski bani, Pavel Banya, etc. Sredna Gora is rich in mineral resources and especially copper. The economy is well developed. The region is an important national hub of copper extraction and processing industry, as well as of optical industry, both centered in and around the town of Panagyurishte. The largest city in Sredna Gora is Stara Zagora, one of the biggest economic centers of Bulgaria.
Sredna Gora has been continuously inhabited for thousands of years. In the 5th millennium BC it was largest mining center in Europe, extracting significant amounts of copper. The mountain range was among the centers of the ancient Thracian civilization, with numerous burial and cult remains being preserved from that period. The renown Thracian Panagyurishte Treasure has been discovered in Sredna Gora. In the Middle Ages the mountain range was part of the Bulgarian Empire since the early 8th century until it was conquered by the Ottoman Turks during the Bulgarian–Ottoman wars in the late 14th century. During the Ottoman rule Sredna Gora was an important center of resistance and the Bulgarian National Revival. It was the focal point of the April Uprising of 1876. Although many settlements in the region were destroyed in the aftermath of the rebellion, it had a decisive role for the subsequent Liberation of Bulgaria in 1878.
Geography Location and limits
Sredna Gora is situated in central Bulgaria, south of and parallel to the Balkan Mountains and north of the Upper Thracian Plain. It extends from the river Iskar in the west to the elbow of the river Tundzha north of the city of Yambol in the east. The main orographic ridge extends from west to east, where the mountain range reaches a total length of 285 km; its maximum width from north to south is 50 km. The total area of Sredna Gora is 5,950 km2. Its highest point is the summit of Golyam Bogdan at 1,604 m; the average elevation is 608 m.
It is part of the Srednogorie mountain system that from west to east includes the mountain ranges of Greben (1,156 m in Bulgarian territory), Zavalska Planina (1,181 m), Viskyar (1,136 m), Lyulin (1,256 m), Vitosha (2,290 m), Plana (1,338 m) and Sredna Gora, as well as the heights of Bakadzhitsite and Hisar further east.
To the north, Sredna Gora extends to eight of the eleven Sub-Balkan valleys — from the southeastern limits of the Sofia Valley in the west, eastwards through the valleys of Saranska, Kamarska, Zlatitsa–Pirdop, Karlovo, Kazanlak, Tvarditsa and Sliven. The valleys of Karlovo and Kazanlak are also collectively known as the Rose Valley. Its easternmost point is the elevation of Zaychi Vrah (256 m) along the southwestern limits of the Sliven Valley just southwest of the bend of the river Tundzha. Along its northern borders, Sredna Gora is linked to the Balkan Mountains through five north-south ridges — Negushevski Rid, Oporski Rid, Galabets, Koznitsa and Strazhata.
To the west, the river Iskar and the Pancharevo Gorge separate Sredna Gora from Plana and the ridges Shipochanski Rid and Shumnatitsa link it to the Rila mountain range. From there, its southern limits follow the northern edge of the Kostenets–Dolna Banya Valley to the Momina Klisura Gorge of the river Maritsa to the town of Belovo. From Belovo begins its border with the Upper Thracian Plain, which roughly follows a line through the settlements of Vetren, Kalugerovo, Blatnitsa, Krasnovo, Starosel, Chernichevo and reaching the river Stryama at the village of Pesnopoy. From there it continues further east close to the villages of Varben, Zelenikovo and Veren, from where the Chirpan Heights from a bulge in southern direction to the town of Chirpan and then the mountain range continues eastwards near Stara Zagora, Korten and Kamenovo, reaching the elevation of Zaychi Vrah northwest of Yambol.
Division
Sredna Gora is divided in three parts by the rivers Topolnitsa and Stryama, both left tributaries of the Maritsa — Ihtimanska Sredna Gora to the west, Sashtinska Sredna Gora in the middle and Sarnena Sredna Gora to the east.
Ihtimanska Sredna Gora is limited to the west by the valley of the Iskar, to the north by the valleys of Sofia, Saranska, Kamarska and Zlatitsa–Pirdop, to the east by the Topolnitsa, to the south by the Rila mountain range. It covers an area of 1,370 km2 with an average elevation of 750 m, thus being the smallest in territory and the highest in average altitude of the three divisions. Ihtimanska Sredna Gora is subdivided in three sections — Vakarelsko–Belishki, Shipochansko–Eledzhiski and Ihitmanski. The first section includes the mountains of Lozen (1,190 m) which is the westernmost point of the whole mountain range, Vakarelska (1,090 m) and Belitsa (1,221 m). The river Gabra forms a small valley between Lozen and Vakarelska. Shipochansko–Eledzhiski section is located between the Samokov Valley in the west and the Topolnitsa in the east and links with Rila and Konstenets–Dolna Banya Valley in the south. It includes the ridges of Shipochanski Rid (1,312 m), Shumnatitsa (1,392 m), Septemvriyski (1,275 m) and Eledzhik (1,186 m). Between these two sections is situated the Ihtiman Valley at an altitude of 620 m to 700 m.
Sashtinska Gredna Gora spans from the valley of the Topolnitsa in the west to the river Stryama in the east. It spans a territory of 2,300 km2 and has an average elevation of 656 m. Sashtinska Sredna Gora is limited to the north by the southern reaches of the Zlatitsa–Pirdop and Karlovo valleys, and to the south by the Upper Thracian Plain. It is subdivided in two sections — Bunaysko–Bogdanski and Panagyursko–Strelchanski. The former is the highest past of the mountain range and is located to the north. From west to east it includes the summits of Bratia (1,519 m), Bunaya (1,572 m) and Golyan Bogdan (1,604 m). In its middle is located the high altitude Koprivshtitsa Valley (1,000 m). The elevation lowers to the south into the valleys of the towns of Panagyurishte and Strelcha, as well as the middle courses of the rivers Luda Yana, Potoka and Pyasachnik.
Sarnena Sredna Gora is the lowest in the range, with most hilly terrain, spanning to the Stryama in the west to the Tundzha in the east. It has an area of 2,280 km2 and an average elevation of 416 m. It is limited to the north by the southern reaches of the valleys of Karlovo, Kazanlak, Tvarditsa and Sliven; in the south it gradually descents to the Upper Thracian Plain. There are three sections — Bratanski, Kortenski and Chirpanski. The former is the highest in elevation, spans from the Stryama in the west to the Zmeyovski Pass (430 m) in the east and is dominated by the summit of Bratan (1,236 m). Kortenski section is located eastwards of the Zmeyovski Pass and reaches the easternmost point of the mountain range at Zaychi Vrah; its highest peak in Moruley (895 m). The third section is formed by the Chirpan Heights located south of Bratanski Section, which reaches a maximum heights of 651 m at Kitka.
Climate
Sredna Gora falls within the temperate continental climatic zone. Yet, the uneven altitude, the significant segmentation and the varied exposure of the relief of Sredna Gora, together with the climate-forming impact of the transformative air masses from the neighbouring territories, determine the marked differentiation of the climatic conditions in the mountain range. The continental climate is prevails in the mountain zone up to 1,000 m along the northern slopes and up to 1,500 m along the southern slopes. Above this elevation the climate is Alpine. In the lower parts of Sarnena Sredna Gora, and especially along its southernmost slopes is the transitional zone between the temperate continental and the continental Mediterranean climate. Due to the uneven altitude, the average January temperature in the lowest parts fluctuates in the range from 0 °C to −4 °C, lowering significantly in the range between −5 °C and −8 °C at higher altitudes. Temperature inversions regularly occur in the well-enclosed valleys in Sredna Gora during winter and have contributed for the absolute minimum temperature at the towns of Panagyurishte (−32.4 °C), Koprivshtitsa (−32.0 °C). and Ihtiman (−31.8 °C).
The significant climatic variation of the mountain range is also manifested by the uneven quantitative distribution of the average annual precipitation and its different regime. In those parts of Sredna Gora with temperate continental and Alpine climate the precipitation has a well-defined summer maximum and a winter minimum. The average annual precipitation in the territory with temperate continental climate varies between 600–800 mm, while in the Alpine zone it reaches 800–1,000 mm. There, together with the increase of altitude and precipitation also increases the amount of solid precipitation, with snow cover reaching an average of four to five months. In the mountain regions in the transitional climatic zone, where the influence of the Mediterranean is stronger, the precipitation is relatively evenly distributed throughout the year and is also the lowest, reaching 550–600 mm annually.
Hydrology
In most of Sredna Gora, the rivers originating from the mountain range have predominantly rain-snow feed and high water in early spring, due to the less pronounces snow retention and the predominantly pluvial element in the river flow, compared to the higher Bulgarian mountain ranges. In its lowest areas in the east, the rivers are almost exclusively with rain feed. Most of these rivers have temporary flow and in places with deforested or eroded watersheds, at times, they also have a pronounced brief torrential flow. In the highest parts of Sredna Gora the river flow is 15 L/s per km2, due to the relatively small amount of precipitation, lower snow retention and stronger evaporation. At lower elevation, particularly in the east, this amount is reduced to 1 L/s per km2, due to the small precipitation, the significant evaporation, the negligible slopes and the permeable ground. The average river flow for the whole mountain range is 4.7 L/s per km2. The water resources in Sredna Gora are more limited compared to other mountain ranges in Bulgaria, due to lower average altitude, higher temperature and lower snow retention.