Danube River in the context of "Moesia Superior"

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.

Moesia (/ˈmiːʃə, -siə, -ʒə/; Latin: Moesia; Greek: Μοισία, romanized: Moisía) was a Roman province situated in the Balkans south of the Danube River. Created after the Danubian-Balkan conquest during the reign of Augustus, Moesia included most of the territory of modern eastern Serbia, Kosovo, north-eastern Albania, northern parts of North Macedonia (Moesia Superior), Northern Bulgaria, Romanian Dobruja and small parts of Southern Ukraine (Moesia Inferior).

The territory of the modern state of Serbia was part of the Roman Empire and later the Eastern Roman Empire. In particular, the region of Central Serbia was under Roman rule for about 800 years (with interruptions), starting from the 1st century BC, interrupted by the arrival of the Slavs into the Balkans during the 6th century, but continued after fall of the First Bulgarian Empire in the early 11th century and permanently ended with the rise of the Second Bulgarian Empire in the late 12th century. The territories were administratively divided into the provinces of Moesia (later Moesia Superior), Pannonia (later Pannonia Inferior) and Dardania. Moesia Superior roughly corresponds to modern Serbia proper; Pannonia Inferior included the eastern part of Serbia proper; Dardania included the western part of Serbia proper. After its reconquest from the Bulgarians by Emperor Basil II in 1018, it was reorganized into the Theme of Bulgaria.

The Danube River influenced the extension of the Roman Empire; its confluents, such as Sava and Morava, affected the growth of frontier fortresses and towns. Many authors and explorers wrote about traces of the Roman Empire on the Danube coast. One of the localities, Felix Romuliana, was ranked on the list of cultural heritage of UNESCO in July 2007.

The Danube Bridge (also known as the Friendship Bridge; Bulgarian: Мост на дружбата, Most na druzhbata or, more commonly, Дунав мост, Dunav most; Romanian: Podul Prieteniei or Podul de la Giurgiu) is a steel truss bridge over the Danube River connecting the Bulgarian bank to the south with the Romanian bank to the north and the cities of Ruse and Giurgiu respectively. It is one of only two bridges connecting Romania and Bulgaria, the other one being the New Europe Bridge between the cities of Vidin and Calafat.

Ice jams occur when the ice that is drifting down-current in a river comes to a stop, for instance, at a river bend, when it contacts the river bed in a shallow area, or against bridge piers. Doing so increases the resistance to flow, thereby inducing an increase in water level upstream of the jam (referred to as backwater). Ice jams are thus a main cause for flooding during the winter. In addition, when the jam is released, depending on the conditions under which this happens, the amount of water that was retained behind the jam can also lead to flooding downstream of where the jam occurred. Ice jam floods are generally less predictable and can also be faster than open-water floods.

The Wachau (German pronunciation: [vaˈxaʊ̯] ) is an Austrian valley formed by the Danube River. It is one of the most prominent tourist destinations of Lower Austria, located between the towns of Melk and Krems that attracts epicureans for its high-quality wines. It is 36 kilometres (22 mi) in length and has been settled since prehistoric times. Among the tourist attractions is Dürnstein Castle, where King Richard I of England was held captive by Leopold V, Duke of Austria. The architectural elegance of its monasteries (Melk Abbey and Göttweig Abbey), castles and ruins combined with the urban architecture of its towns and villages, and the cultivation of vines as an important agricultural produce are the dominant features of the valley.

The Wachau was inscribed as "Wachau Cultural Landscape" in the UNESCO List of World Heritage Sites in recognition of its architectural and agricultural history, in December 2000.