Source of the Tagus River Nature · Frías de Albarracín, Sierra de Albarracín, Teruel Image of Frías de Albarracín, not of the place itself. The point where the Tagus, the longest river on the Iberian Peninsula, rises at the Fuente García, within the municipal boundary of Frías de Albarracín (Teruel), at an altitude of 1,593 metres, between the peaks of the Muela de San Juan (1,830 m) and the Cerro de San Felipe (1,839 m). The source lies in the Sierra de Albarracín, within the Montes Universales, the western branch of the Iberian System and one of the peninsula's most important watersheds between the Atlantic and Mediterranean slopes. In its first ten kilometres the river drops 453 metres in elevation. In 1974 a monument commemorating the river's source was erected at a lower altitude. Photo: 19Tarrestnom65 (CC BY-SA 4.0) What to see and do in Frías de Albarracín