The River Ebro has the greatest discharge of any Iberian river, and is the longest in Spain, and second only to the Tajo ( Tagus, in thoery, in English) in Iberia . Its importance is reflected in the name of Peninsula, which almost certainly comes from the river, first known as the Iber and Iberus and Ebro, and not the other way around. It was first used in the 6th century BC by a Greek author in reference to the Iberians, or the people who lived along the Iberus ( Ebro ) river. Ultimately the word may well derive from the Basque words ibai (river) and ibar (valley), and these from ur meaning water. Linguists have noted similarities with the names of 200 other European rivers and streams (e.g. Ibar in Serbia, Ebrach and several Eberbach in Germany, Irwell in The UK) giving a tantalising clue as to a form of Basque being once spoken throughout Europe before the arrival of Indo-European tribes and languages.