Which river is the longest in the Iberian Peninsula?

The longest river in the Iberian Peninsula is the Tagus.

Known as the Tajo in Spanish and the Tejo in Portuguese, the Tagus flows for roughly 1,000 kilometres from the Montes Universales in eastern Spain to the Atlantic Ocean at Lisbon. It travels westward across Spain, then forms part of the Spain–Portugal border before continuing through Portugal.

The river has shaped the history and geography of both countries. It passes important cities including Toledo, where it loops dramatically around the old city, and Lisbon, whose broad estuary opens into the Atlantic. Its basin is one of the peninsula’s most heavily populated and includes the Madrid metropolitan area.

A common mix-up is the Douro, or Duero, which is also a major Iberian river and crosses Spain and Portugal. The Ebro is longer than some other Spanish rivers but lies mainly in northeastern Spain and does not exceed the Tagus. Reservoirs and water transfers have significantly altered the Tagus’s natural seasonal flow.