It was the conquest by Rome that made Britain part of one of the greatest civilisations of ancient times. Rome began as a walled market-place and fortress for its citizens, who farmed the country round. They had a strong feeling for order, system, and discipline; and in the course of five or six centuries they mastered first the neighbouring cities, then the rest of Italy, and eventually all the Mediterranean countries. Their Republic became a monarchy, under an Emperor, who could inspire loyalty in the great professional army that was now needed to defend these conquests.