Which river is known as the principal river of the Iberian Peninsula?

The Tagus River is recognized as the principal river of the Iberian Peninsula, which encompasses both Spain and Portugal. It has significant historical, cultural, and economic importance in the region. The Tagus originates in the Sierra de Albarracín mountain range in Spain and flows westward across the country before emptying into the Atlantic Ocean near Lisbon, Portugal. As the longest river on the peninsula, it has played a crucial role in transportation, agriculture, and city development throughout history.

This river is not only vital for its water resources but also for its cultural heritage, as various cities along its banks, notably Toledo and Lisbon, have been shaped by the river's presence. Conversely, the Rhine, Seine, and Elbe rivers, while notable in Europe, serve other geographical regions and do not flow through the Iberian Peninsula, thus making them unsuitable as the principal river in that context.