Ebro, The (anciently the Iberus), the chief river of Spain, rises in the province of Santander in the Cantabrian Mountains, and flows S.E. through Old Castile, Navarre, Aragon, and Catalonia, falling into the Mediterranean, after a course of more than 300 miles, 80 miles S.W. of Barcelona. Although navigable for 180 miles from the mouth, its course is obstructed by rapids and shallows, to avoid which a canal has been made for nearly 100 miles along the bank, and there is another canal through the delta. The Ebro receives several tributaries.