The Portuguese wine-growing region is named after the 900-kilometre-long river of the same name, on whose often very steep slopes with extreme inclination the vineyards are located. The river has its source in the Spanish province of Soria(Castilla y León), flows through northern Spain as the "Duero" and then through northern Portugal as the "Douro" until it finally flows into the Atlantic Ocean at the city of Porto. The river forms the Portuguese-Spanish border for more than 100 kilometres, after which the port wine region extends into Portugal for the same length of time.
As early as 1756, under the then Prime Minister Marquês de Pombal (1699-1782), in order to protect the authenticity of port wine, the Douro region was first defined within its boundaries as one of the oldest protected wine regions in the world and later classified as a DOC area. However, the "Vinho do Porto" or "Porto" is not named after its Douro region of origin, but after the port city from which it is shipped. For more than two centuries, this applied exclusively to port wine. It was not until 1979 that this was extended to include unpritified wines. The success of the famous red wine "Barca Velha" from the Ferreira winery, but later also of the "Redomo" from Niepoort and the "Grande Escolha" from Quinta do Côtto contributed to this success.
Like all waters, the river has a positive effect on viticulture or creates the conditions for it by forming valley slopes. It is actually a double appellation, where "Douro = normal wine" and "Porto e Douro = port wine". In 2001, the classic port wine area Douro (Alto Douro) was declared a World Heritage Site by UNESCO. Of the total area of almost 40,000 hectares, 33,000 hectares are classified for port wine (slate soils) and 7,000 hectares for normal wine (granite soils). However, about half of them are also processed as normal wines by the port wine areas, depending on the quality of the vintage. The grape varieties are practically the same as for port wine. The recommended ones must be at least 60%. Wines of non-approved varieties are marketed as country wines (Vinho Regional) under the name Duriense. Many wineries produce both Port wines and normal wines. See a list of well-known producers under the keyword Port wine.
Map: From Rei-artur - Own work, CC BY 2.5, Link
Douro Valley above: By Bruno Rodrigues, CC BY-SA 3.0, Link
Douro Valley below: Symington