Tagus

The Tagus ( ; ; ; ) is the longest river in the Iberian Peninsula. The river rises in the Montes Universales in mid-eastern Spain, flows , generally west with two main south-westward sections, to empty into the Atlantic Ocean near Lisbon. Its drainage basin covers – exceeded in the peninsula only by the Douro. The river is highly used. Several dams and diversions supply drinking water to key population centres of central Spain and Portugal; dozens of hydroelectric stations create power. Between dams it follows a very constricted course, but after Almourol, Portugal it has a wide alluvial valley, prone to flooding. Its mouth is a large estuary culminating at the major port, and Portuguese capital, Lisbon.
The source is specifically: in political geography, at the Fuente de García in the Frías de Albarracín municipality; in physical geography, within the notably high range, the Sistema Ibérico (Iberian System), of the Sierra de Albarracín Comarca. All the major tributaries are right bank, which is locally to the north. The river flows in Spain, along the two countries' border and in Portugal.
The main cities the rivers passes through consecutively are Aranjuez, Toledo and Talavera de la Reina in Spain, and Abrantes, Santarém, Almada and Lisbon in Portugal. The Spanish capital, Madrid, lies in the upper drainage basin.
Course.
In Spain.
The first notable city on the Tagus is Sacedón. Below Aranjuez it receives the combined flow of the Jarama, Henares, Algodor and Tajuña. Below Toledo it receives the Guadarrama River. Above Talavera de la Reina it receives the Alberche. At Valdeverdeja is the upper end of the long upper reservoir, the "Embalse de Valdecañas", beyond which are the "Embalse de Torrejon", into which flow the Tiétar, and the lower reservoir, the Alcántara Dam into which flows the Alagón at the lower end.
A canal and aqueduct are between the Tagus and the Segura for the Tagus-Segura Water Transfer.
In Portugal.
After forming the border it enters Portugal, passing Vila Velha de Ródão, Abrantes, Constância, Entroncamento, Santarém and Vila Franca de Xira at the head of the long narrow estuary, which has Lisbon at its mouth. The estuary is protected by the Tagus Estuary Natural Reserve. There is a large bridge across the river, the Vasco da Gama Bridge, which with a total length of is the second longest bridge in Europe. The Port of Lisbon, straddling its mouth, is one of Europe's busiest.
The Portuguese Alentejo region and former Ribatejo Province take their names from the river; Alentejo, from "além Tejo" "Beyond the Tejo" and Ribatejo likely from "arriba Tejo", an archaic way of saying "Upper Tejo". However Spanish means riverside, or riviera. If from that root Ribatejo would mean very generically "Tejo-side". Many instances of towns in Spain have this prefix.
Name.
The river's Latin name is "Tagus" and it is known under different names in the languages of Iberia:
It is known in Italian as and Greek as ("Tágos").
Geology.
The lower Tagus is on a fault line. Slippage along it has caused numerous earthquakes, the major ones being those of 1309, 1531 and 1755.
History.
The Pepper Wreck, properly the wreck of the "Nossa Senhora dos Mártires", is a shipwreck located and excavated at the mouth of the Tagus between 1996 and 2001.
The river had strategic value to the Spanish and Portuguese empires, as it guarded the approach to Lisbon. For example, in 1587, Francis Drake briefly approached the river after his successful raid at Cadiz.
Popular culture.
A major river, the Tagus is brought to mind in the songs and stories of the Portuguese. A popular fado song in Lisbon notes that while people get older, the Tagus remains young ("My hair getting white, the Tagus is always young"). The author, Fernando Pessoa, wrote a poem that begins: 
Richard Crashaw (died 1649) wrote a poem "Saint Mary Magdalene, or the Weeper". This refers to the "Golden" Tagus as wanting Mary Magdalene's silver tears. In classical poetry the Tagus was famous for its gold-bearing sands (the catalogued works of: Catullus 29.19; Ovid's "Amores" 1.15.34; Juvenal's "Satires" 3.55; and others).