EBRO (in Latin Iberus), 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° 4Γ 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, and seafaring 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.