The Tagus (Latin Tagus, Spanish Tajo, Portuguese Tejo, pron. IPA: ['tɛʒʊ], Ancient greek Tàghos, Ταγος) is the longest river on the Iberian Peninsula. It measures 1,038 kilometers in length, 716 km of which are in Spain, 47 km as borer between Portugal and Spain and the remaining 275 km in Portugal, where it empties into the Atlantic at Lisbon. It drains an area of 80,100 km² (the second largest in the Iberian peninsula after the Douro). It follows a very constricted course for much of its length, but after Almourol it enters a vast alluvial valley prone to flooding. Today the Alcantara Dam regulates much of the river's flow.