Danubian plain

The Danubian Plain extends from the western borders to the Black Sea. It encompasses the area between the Danube River, which forms most of the country's northern border, and Stara Planina to the south. The plateau slopes gently from cliffs along the river, then it abuts mountains of 750 to 950 m. The plateau, a fertile area with undulating hills, is the granary of the country.

Stara Planina

The southern edge of the Danubian Plain blends into the foothills of Stara Planina, sometimes thought of as the Bulgarian part of the Carpathian Mountains. The Carpathians resemble a reversed S as they run eastward from the Czech Republic and Slovakia across the northern portion of Romania, swinging southward to the middle of Romania and then running westward, where they are known as the Transylvanian Alps. The mountains turn eastward again at the Iron Gate, a gorge of the Danube River at the Romanian-Serbian border. At that point, they become Stara Planina of Bulgaria.

Stara Planina originates at the Timok Valley in Serbia and run southward towards the Sofia Basin in west central Bulgaria. From there they run east to the Black Sea. The Balkans are about 600 km long and 30 to 50 km wide. They retain their height well into central Bulgaria, where Botev Peak, the highest point in the Balkan Mountains, rises to about 2,376 m. The range then continues at lower altitude to the cliffs of the Black Sea. Through most of Bulgaria, the Balkans form the watershed from which rivers drain north to the Danube River or south to the Aegean Sea. Some smaller rivers in the east drain directly to the Black Sea. The Sredna Gora is a narrow ridge about 160 km long and 1,600 m high, running east to west parallel to the Balkans. Nested between both ranges is the Rose Valley, famous for rose oil used in perfume and liqueurs.

Subbalkan Valleys and Thracian Plain

The southern slopes of the Balkan Mountains and the Sredna Gora give way to the Thracian Plain and the Sofia Basin. Roughly triangular in shape, the Thracian Plain originates at a point east of the mountains near Sofia and broadens eastward to the Black Sea. It includes the Maritsa valley and the lowlands that extend from the river to the Black Sea. Like the Danubian Plateau, much of the Thracian Plain is somewhat hilly and not a true plain. Most of its terrain is moderate enough to cultivate.

The largest basin in Bulgaria is the Sofia Basin. About 24 km wide and 96 km long, the basin contains the capital city and the area immediately surrounding it. The route through basins and valleys from Belgrade to Istanbul (formerly Constantinople) via Sofia has been historically important since Roman times, determining the strategic significance of the Balkan Peninsula. Bulgaria's largest cities were founded on this route. Paradoxically, although the mountains made many Bulgarian villages and towns relatively inaccessible, Bulgaria has always been susceptible to invasion because no natural obstacle blocked the route through Sofia.

Rilo-Rhodope massif

Relatively high mountains occupy the area between the Thracian Plain and Sofia Basin and the Greek border to the south. The western parts consist of three ranges: the Vitosha Mountain south of Sofia, the Rila Mountains further south, and the Pirin Mountains in the southwestern corner of the country. They are the most outstanding topographic feature of Bulgaria and of the entire Balkan Peninsula. The Rila range includes Mount Musala, whose 2,925-metre peak is the highest in any Balkan country. About a dozen other peaks in Rila are over 2,600 meters. The highest peaks are characterized by sparse bare rocks and remote lakes above the tree line. The lower peaks, however, are covered with alpine meadows that give the range an overall impression of green beauty. The Pirin range is characterized by rocky peaks and stony slopes. Its highest peak is Mount Vihren, at 2,915 meters the second-highest peak in Bulgaria. Further east are the extensive Rhodope Mountains.