A classic theory introduced by Pliny the Elder, was that the river originated from the Lagunas de Ruidera and divided into two branches: the Upper Guadiana () and the Guadiana, while separated by a subterranean course. This legend developed from a misguided belief (which persisted until the 19th century) that the river appeared and disappeared over time, because of its subterranean tributary. In fact, no subterranean course exists, and the belief that the Lagunas de Ruidera is the source is also controversial. toponymically and traditionally the Upper Guadiana, which runs from Viveros (Albacete) until Argamasilla de Alba (Ciudad Real) had been identified as the main branch of the Guadiana. But even hydro-geological characteristics indicate that the Upper Guadiana may not be the principal river within the system.