Danubian Plain (Bulgaria) in the context of "East European Plain"

The Iskar (Bulgarian: Искър, pronounced [ˈiskɐr]; Latin: Oescus) is a right tributary of the Danube. With a length of 368 km, it is the longest river that runs entirely within Bulgaria. Originating as three forks in Balkan's highest mountain range Rila, the Iskar flows in a northern direction until its confluence with the Danube. As it flows northwards it fuels the largest artificial lake in the country, the Iskar Reservoir, forms the divide between the Vitosha and Plana Mountains in the west and the Sredna Gora mountain range in the east before entering the Sofia Valley, which contains the nation's capital Sofia. From there the Iskar runs through the Balkan Mountains, forming the spectacular 84 km long Iskar Gorge. As it crosses the mountains, its water course turns in a north-eastern direction at Lakatnik. North of the Balkan Mountains, the river crosses the Danubian Plain and finally flows into the Danube between the villages of Baykal and Gigen. Geologically, Iskar is the oldest river in the Balkan Peninsula.

Its watershed drains 8,617 km in the provinces of Sofia, Sofia City, Vratsa, Lovech and Pleven. The Iskar flows through nine towns and numerous villages. The Iskar river basin is home to more than 50 species of fish, including Cottus haemusi that is endemic to the upper Iskar and Vit drainages.

The Seven Slavic tribes (Bulgarian: Седемте славянски племена, romanized: Sedemte slavyanski plemena), or the Seven clans (Bulgarian: Седемте рода, romanized: Sedemte roda) were a union of Slavic tribes in the Danubian Plain, that was established around the middle of the 7th century and took part in the formation of the First Bulgarian Empire together with the Bulgars in 680−681.

Since its establishment, it faced attacks from the Byzantine Empire. The Bulgars crossed the Danube and in the 670s they concluded an alliance with the Slavic Union. Theophanes writes that the Bulgars became masters of the Slavs. The Slavic Union recognized the sovereignty of Khan Asparuh and together, in the spring of 681, they won a major victory over the Byzantines.

Northern Bulgaria (Bulgarian: Северна България, romanized: Severna Bylgarija), also called Moesia (Bulgarian: Мизия, Mizija) is the northern half of Bulgaria, located to the north of the main ridge of the Balkan Mountains which conventionally separates the country into a northern and a southern part. Besides the Balkan Mountains, Northern Bulgaria borders the Timok River and Serbia to the west, the Danube River and Romania to the north, and the Bulgarian Black Sea Coast to the east.

Geographically, the region's terrain is relatively uniform, dominated by the hilly Danubian Plain, with some low plateaus to the east. Northern Bulgaria covers an area of 48,596 square kilometres and has a population of 2,674,347 according to the 2011 census (36% of Bulgaria's entire population), with a population density of 55 people per km². The three largest cities are Varna, Rousse and Pleven.

43°30′N 26°45′E / 43.500°N 26.750°E / 43.500; 26.750

The Ludogorie (Bulgarian: Лудогорие) or Deliorman (Делиорман; Turkish: Deli Orman, lit. 'mad forest' and Bulgarian: lud - "mad", "crazy" and gora - "forest"), is a region in northeastern Bulgaria stretching over the plateau of the same name. Major cities in the region are Targovishte, Razgrad, Dulovo, Novi Pazar, Pliska, Preslav, and Isperih. Part of the Danubian Plain, the region is hilly in the east, reaching up to 485.70 metres (1,593.5 ft) in height near the village of Samuil, but merges with the plains of Dobruja and the Danube to the north, with the lowest point near Yuper (39.14 m (128.4 ft)). The region is bordered to the west by the Provadiya River and the Beli Lom; to the east it transitions into the Dobruja plateau. The region has a significant ethnic Turkish minority.

The Romanian Plain (Romanian: Câmpia Română) is located in southern Romania and the easternmost tip of Serbia, where it is known as the Wallachian Plain (Serbian: Влашка низија, romanized: Vlaška nizija). It is part of the larger Eurasian Steppe. It is located in the historical region of Wallachia, and bordered by the Danube River in the east, south, and west and by the Getic Plateau in the north. Bucharest, the capital of Romania, is located in the central part of the Romanian Plain. It is contiguous to the south with the Danubian Plain (Bulgarian: Дунавска равнина, romanized: Dunavska ravnina) in Bulgaria. The Romanian Plain is also sometimes referred to as the Danubian Plain (Câmpia Dunării) in the Romanian language, though this designation is not specific, because the Danube flows through a number of plains along its course, including the Hungarian Plain (which is called the Danubian Plain in Slovakia and Serbia), as well as the Bavarian Lowland, which is also sometimes called the Danubian Plain.

The Lom (Bulgarian: Лом [ˈɫɔm], Latin: Almus) is a river in the western part of the Danubian Plain of northwestern Bulgaria. A right tributary of the Danube, the river is 93 km long.

Pliska (Bulgarian: Плиска [ˈpliskɐ], Old Bulgarian: Пльсковъ, romanized: Plĭskovŭ) was the first capital of the First Bulgarian Empire during the Middle Ages and is now a small town in Shumen Province, on the Ludogorie plateau of the Danubian Plain, 20 km northeast of the provincial capital, Shumen.

Pliska was the first capital of Bulgaria. According to legend, it was founded by Asparuh of Bulgaria in the late 7th century; this legend is archaeologically unsubstantiated. The site was originally an encampment, with the first tent-shaped buildings at Pliska of uncertain date. No evidence exists of a settlement before the 9th century, and claims that the site dates from Late Antiquity have been contested.