The Tagus (/ˈtɡəs/ TAY-gəs; Spanish: Tajo [ˈtaxo]; Portuguese: Tejo [ˈtɛʒu]; see below) is the longest river in the Iberian Peninsula. The river rises in the Montes Universales in mid-eastern Spain, flows 1,007 km (626 mi), generally west with two main south-westward sections, to empty into the Atlantic Ocean near Lisbon. Its drainage basin covers 80,100 square kilometers (30,927 sq mi) exceeded in the peninsula only by the Douro. The river is highly used. Several dams and diversions supply drinking water to key population centres of central Spain and Portugal; dozens of hydroelectric stations create power. Between dams it follows a very constricted course, but after Almourol, Portugal it has a wide alluvial valley, prone to flooding. Its mouth is a large estuary culminating at the major port, and Portuguese capital, Lisbon.

Tajo  (Spanish)
Tejo  (Portuguese)
View of Tagus River in Toledo, Spain
Path of the Tagus through the Iberian Peninsula
EtymologyVulgar Latin taliāre, "to cut through"
CountrySpain, Portugal
Physical characteristics
SourceFuente de García
  locationMontes Universales, Sierra de Albarracín Comarca, Teruel, Aragon, Spain
  elevation1,593 m (5,226 ft)
MouthEstuary of the Tagus
Atlantic Ocean near Lisbon, Portugal
0 m (0 ft)
Length1,007 km (626 mi)
Basin size80,100 km2 (30,900 sq mi)
  average500 m3/s (18,000 cu ft/s)
Basin features
  leftGuadiela, Algodor, Gévalo, Ibor, Almonte, Salor, Sever
  rightGallo, Jarama, Guadarrama, Alberche, Tiétar, Alagón, Zêzere
Tagus river gorge, in the Alto Tajo Nature Reserve, Guadalajara, Spain
The Tagus near Vila Velha de Ródão, close to the Spanish border

The source is specifically: in political geography, at the Fuente de García in the Frías de Albarracín municipality; in physical geography, within the notably high range, the Sistema Ibérico (Iberian System), of the Sierra de Albarracín Comarca. All the major tributaries are right bank, which is locally to the north. The river flows 716 km (445 mi) in Spain, 47 km (29 mi) along the two countries' border and 275 km (171 mi) in Portugal.

The main cities the rivers passes through consecutively are Aranjuez, Toledo and Talavera de la Reina in Spain, and Abrantes, Santarém, Almada and Lisbon in Portugal. The Spanish capital, Madrid, lies in the upper drainage basin.