The Latinized name Durius, likely came from the Celtic tribes that inhabited the area before Roman times: the Celtic root is *dubro-. In modern Welsh, dŵr is "water," as well as dour in modern Breton with cognate dobhar in Irish. In Roman times, the river was personified as a god, Durius.
The Douro vinhateiro (winegrowing), an area of the Douro Valley in Portugal long devoted to vineyards, has been designated by UNESCO as a World Heritage Site. Traditionally, the wine was taken down river in flat-bottom boats called rabelos, to be stored in barrels in cellars in Vila Nova de Gaia, just across the river from Porto. In the 1950s and 1960s, dams were built along the river, which ended this river traffic from the upper regions in Spain and along the border. Now Port wine is transported in tanker trucks.
In 1998, Portugal and Spain signed the Albufeira Convention, an agreement on the sharing of trans-boundary rivers to include the Douro, Tagus and Guadiana. The convention superseded an original agreement on the Douro, signed in 1927, that was expanded in 1964 and 1968 to include tributaries.
It is the third-longest river in the Iberian Peninsula after the Tagus and Ebro. Its total length is 897 kilometres (557 mi), of which only sections of the Portuguese extension below the fall line are navigable, by light rivercraft.
In its Spanish section, the Douro crosses the great Castilian meseta and meanders through five provinces of the autonomous community of Castile and León: Soria, Burgos, Valladolid, Zamora, and Salamanca, passing through the towns of Soria, Almazán, Aranda de Duero, Tordesillas, and Zamora.
In this region, there are few tributaries of the Douro. The most important are the Pisuerga, passing through Valladolid, and the Esla, which passes through Zamora. This region is generally semi-arid plains, with wheat and in some places, especially near Aranda de Duero, with vineyards, in the Ribera del Duero wine region. Sheep rearing is also still important.
For 112 kilometres (70 mi), the river forms part of the national border line between Spain and Portugal, in a region of narrow canyons. It formed a historical barrier to invasions, creating a cultural/linguistic divide. In these isolated areas, in which the Aldeadávila Dam impounds the river, there are protected areas: the International Douro Natural Park (on the Portuguese side) and the Arribes del Duero Natural Park (on the Zamoran margin).
The Douro fully enters Portuguese territory just after the confluence with the Águeda River; once the Douro enters Portugal, major population centres are less frequent along the river. Except for Porto and Vila Nova de Gaia at the river mouth, the only population centres of any note are Foz do Tua, Pinhão and Peso da Régua. Tributaries here are small, merging into the Douro along the canyons; the most important are Côa, Tua, Sabor, Corgo, Tavora, Paiva, Tâmega, and Sousa. None of these small, fast-flowing rivers is navigable.
Major Spanish riverside towns include Soria, Almazán, Aranda de Duero, Tordesillas, Zamora and major Portuguese towns include Miranda do Douro, Foz Côa, Peso da Régua, Lamego, Vila Nova de Gaia, and Porto. The most populous cities along the Douro River are Valladolid and Zamora in Spain, and Porto and Vila Nova de Gaia in Portugal. The latter two are located at the mouth of the Douro at the Atlantic Ocean.
In Portugal, the Douro flows through the districts of Bragança, Guarda, Viseu, Vila Real, Aveiro and Porto. Porto is the main hub city in northern Portugal. Its historic centre has been designated as a UNESCO World Heritage Site because of its significant architecture and history.
These reaches of the Douro have a microclimate allowing for cultivation of olives, almonds, and especially grapes, which are important for making the famous Port wine. The region around Pinhão and São João da Pesqueira is considered to be the centre of Port wine, with its quintas (or farms/estates) that extend along the almost vertical slopes of the steep river valleys. In the 21st century, many of these quintas are owned by multinational wine companies.
Recently, a prosperous tourist industry has developed based on river excursions from Porto to points along the Upper Douro valley.
The Douro railway line (in Portuguese: Linha do Douro) was completed in 1887; it connects Porto, Rio Tinto, Ermesinde, Valongo, Paredes, Penafiel, Livração, Marco de Canaveses, Régua, Tua and Pocinho. Pocinho is near the city of Foz Côa, which is close to Côa Valley Paleolithic Art site. This is considered important to the archaeological pre-historic patrimony, and it has been designated as a UNESCO World Heritage Site.
Fifteen dams have been built on the Douro to regulate the water flow, generate hydroelectric power, and allow navigation through locks. Beginning at the headwaters, the first five dams are in Spain: Cuerda del Pozo, Los Rábanos, San José, Villalcampo and Castro Dams. The next five downstream are along the Portuguese-Spanish border; the first three are owned and operated by Portugal: (Miranda, Picote and Bemposta Dams), while the next two belong to Spain: (Aldeadávila and Saucelle Dams). The Douro's last five dams are in Portugal, and allow for navigation: Pocinho, Valeira, Régua, Carrapatelo and Crestuma-Lever Dams. Vessels with a maximum length of 83 metres (272 ft) and width of 11.4 metres (37 ft) can pass through the five locks. The highest lock, at Carrapatelo Dam, has a maximum lift of 35 metres (115 ft). The waters of Pocinho lake reach 125 metres (410 ft) above sea level.