Which 1,007 km river is the longest on the Iberian Peninsula? The answer is the Tagus.
The Tagus rises at Fuente García in the Montes Universales of central-eastern Spain and runs generally west for about 1,007 km. It crosses Spain and Portugal before reaching the Atlantic through the broad Tagus Estuary at Lisbon. Its route makes it the longest river on the Iberian Peninsula.
In Spanish it is the Tajo, while in Portuguese it is the Tejo. The river has long been important to settlement, agriculture, transport, and water management in both countries. Major cities on or near its course include Toledo and Lisbon, and reservoirs along the river regulate water supplies and electricity generation.
The main confusion is with the Ebro, Douro, and Guadiana, all major Iberian rivers. The Ebro is the peninsula’s longest river that flows into the Mediterranean, while the Douro and Guadiana also cross the Spanish-Portuguese region. “Longest on the peninsula” refers to total river length, not discharge or basin area.