The Guadalquivir (ˌɡwɑːdəlkɪˈvɪər, also UK-kwɪˈ-, US-kiːˈ-,_ˌɡwɑːdəlˈkwɪvər, ɡwaðalkiˈβiɾ) is the fifth-longest river in the Iberian Peninsula and the second-longest river with its entire length in Spain. The river is the only major navigable river in Spain. Currently it is navigable from Seville to the Gulf of Cádiz, but in Roman times it was navigable from Córdoba.
The river is long and drains an area of about . It rises at Cañada de las Fuentes (village of Quesada) in the Cazorla mountain range (Jaén), flows through Córdoba and Seville and reaches the sea between the municipalities of Almonte and the fishing village of Bonanza, in Sanlúcar de Barrameda, flowing into the Gulf of Cádiz, in the Atlantic Ocean.
The marshy lowlands at the river's mouth are known as "Las Marismas". The river borders the Doñana National Park reserve.
The modern name of Guadalquivir comes from the Arabic al-wādī l-kabīr (اَلْوَادِي الْكَبِيرْ), meaning "the big river".
There was a variety of names for the Guadalquivir in Classical and pre-Classical times. According to Titus Livius (Livy), The History of Rome, Book 28, the native people of Tartessians or Turdetanians called the river by two names: Certis (Kertis) and Rherkēs (Ῥέρκης). Greek geographers sometimes called it "the river of Tartessos", after the city of that name. The Romans called it by the name Baetis (which was the basis for name of the province of Hispania Baetica).
During a significant portion of the Holocene, the western Guadalquivir valley was occupied by an inland sea, the Tartessian Gulf.
The Phoenicians established the first anchorage grounds and dealt in precious metals. The ancient city of Tartessos (that gave its name to the Tartessian Civilization) was said to have been located at the mouth of the Guadalquivir, although its site has not yet been found.
The Romans, whose name for the river was Baetis, settled in Hispalis (Seville), in the 2nd century BC, making it into an important river port. By the 1st century BC, Hispalis was a walled city with shipyards building longboats to carry wheat.