The fourth and last region of Catalonia is the inland, which looks not towards the Mediterranean but to the Ebro and Aragon. It is drained by the Segre, an important stream, which after being joined by its tributaries, the Noguera and the Pallaresa, falls into the Ebro not far to the south of Lerida. The tracts around that town are flat and fertile, part of the main valley of the Ebro. But the head-waters of the Segre and its affluents flow through narrow and difficult mountain valleys, starting in the highest and wildest region of the Pyrenees. They are very inaccessible, and served by no roads suitable for the use of an army. Hence, like the upper valley of the Llobregat, they served as places of refuge for the Catalan insurgents when Lerida and the flat country had been lost. The only place of importance in these highlands is the remote town of Seu d’ Urgel[294], a mediaeval fortress near the sources of the Segre, approached by mule-paths only, and quite lost in the hills. [294] Urgel is more accessible from France than from Spain. The easiest path to it is that which, starting from Mont-Louis, crosses the Spanish frontier at Puycerda, and follows the head-water of the Segre to the foot of the hill on which the Seu stands. Catalonia, then, is pre-eminently a mountain land, and one presenting special difficulties to an invader, because it has no central system of roads or valleys, but is divided into so many heterogeneous parts. Though not fertile, it was yet rich, and fairly well peopled when compared with other regions of Spain[295]. Its wealth came not from agriculture but from commerce and manufactures. Barcelona, a city of 180,000 souls, was the greatest Mediterranean port of Spain: on each side of it, along the coast, are dozens of large fishing-villages and small harbour-towns, drawing their living from the sea. Of the places which lay farther back from the water there were many which made an ample profit from their manufactures, for Catalonia was, and still remains, the workshop of Spain. It is the only province of the kingdom where the inhabitants have developed industries on a large scale: its textile products were especially successful, and supplied the whole Peninsula. [295] The population of the Principality in 1803 was 858,000 souls.