The Tagus is a river that runs through Spain and Portugal. It is the longest river in the Iberian Peninsula, with a length of 1, 007 km. It is also the second longest river in the Iberian Peninsula after the Douro. The Tagus is an important source of water for both countries, and it is used for irrigation, navigation, and hydroelectric power generation. The river has been an important part of the history and culture of both countries, and it is a popular tourist destination.