The next Roman leader to be sent to Britain was Publius Ostorius Scapula; and under him the theatre of war shifted to the north and west, those parts of the island which had hitherto remained practically unexplored. The nature of the struggle likewise changed. The tribes hitherto encountered by the {25} Romans were closely akin to the people of Gaul, and their civilization also was very similar in quality. They were people who valued peace and commerce, and who, when they had recovered from the first shock of outraged independence, were content to become Roman tributaries. But the tribes inhabiting the Welsh mountains were far less civilized. Of trade they knew practically nothing, and very little about the settled pursuit of agriculture. But they loved freedom, and were prepared again and again to rise in its defence. The first task which Ostorius set himself was the conquest of the Decangi who dwelt, according to Tacitus, on the shore of the Irish Sea. He raided their territory; but before anything like a conquest had been effected he was called away to deal with the far more turbulent and warlike Silures of the south. These were the inhabitants of Monmouth and Glamorgan; and they were now under the leadership of the famous Caratacus. This able man had concluded an alliance with the neighbouring Ordovices, and the united tribes were able to offer a stiff resistance to Roman aggression. It was not until the war had lasted many years, and Caratacus had won several victories, {26} that the persistence and the superior science of Ostorius were rewarded with success. The site of the final battle is uncertain, but it may well have been near Church Stretton at the spot now called Caer Caradoc. At this battle Caratacus was defeated and taken prisoner, later to be led in triumph through the streets of Rome. This was probably in the year A.D. 51. To keep the Silures in subjection the first of the great Roman forts in Wales was erected at Caerleon on the river Usk.