EBRO (in Latin lberus), the principal river of Spain, rises in the Cantabrian Mountains, near Reinosa, in the province of Santander, flows in a general south-east direction through Old Castile, Navarre, Aragon, and Catalonia, and falls into the Mediterranean about 80 miles south-west of Barcelona, in 40° 41' N. lat. and 0° 50' E. long., forming by its delta a very considerable excrescence on the otherwise regular outline of the coast. It has a total length of about 340 miles, and its drainage area is calculated at 31,445 square miles. Already a noble stream when it breaks through the pass of Horadada, it becomes navigable about Tudela ; but its value as a means of communication is almost neutralized by the obstacles in its channel, a,nd sea-faring vessels cannot proceed further up than Tortosa. The great Imperial Canal, commenced by the emperor Charles V., proceeds along the right bank of the river from a point about three miles below Tudela, to the monastery of Monte Terero, five miles below Saragossa ; and the San Carlos Canal affords direct communication between Amposta at the head of the delta and the harbour of Los Alfaques. The principal tributaries of the Ebro are - from the right hand the Jalon with its affluent the Jiloca, the Huerva, the Aguas, the Martin, and the Guadalope ; from the left the Aragon, the Gallago, and the Segre with its elaborate system of confluent rivers.