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 1,604 m (5,262 ft). 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 Topolnitsa is a river in southern Bulgaria, an important left tributary of the Maritsa. The river's name is derived from the Bulgarian word топола, topola ("poplar"). Reaching length of 155 km, the Topolnitsa is the fourth longest river in the Maritsa drainage, following the Tundzha (390 km), the Arda (290 km) and the Ergene (281 km).