SEGURA (anc. Tader)  , a river of south-eastern Spain about 150 M. long . It is formed by the confluence of three head-streams, one of which rises on the northern versant of La Sagra (7875 ft.), a mountain in Granada, while the other two spring from the Sierra de Segura, in Jaen . From the junction of these three streams below Yeste the river winds in an easterly and south-easterly direction past the towns of Cieza and Archena to Murcia . Thence it trends N.E. and passing Orihuela falls into the Mediterranean 19 m . S.W. of Alicante . Its chief tributaries are the Mundo and Arroyo del Jua on the left, and the Caravaca, Quipar and Sangonera on the right . It is only navigable by small sailing-vessels, even in its estuary, but its waters are extensively utilized fcr irrigation .