The Norman Conquest was not, however, a mere change of dynasty. It led to at least three other changes of the utmost importance. It added a new element to the population, it brought England into contact with the central and southern countries of the Continent, instead of merely with the northern as before, and it made the central government of the country vastly stronger. There is no satisfactory means of discovering how many Normans and others from across the Channel migrated into England with the Conqueror or in the wake of the Conquest, but there is no doubt that the number was large and their influence more than proportionate to their numbers. Within the lifetime of William, whose death occurred in 1087, of his two sons, William II and Henry I, and the nominal reign of Stephen extending to 1154, the whole body of the nobility, the bishops and abbots, and the government officials had come to be of Norman or other continental origin. Besides these the architects and artisans who built the castles and fortresses, and the cathedrals, abbeys, and parish churches, whose erection throughout the land was such a marked characteristic of the period, were immigrants from Normandy. Merchants from the Norman cities of Rouen and Caen came to settle in London and other English cities, and weavers from Flanders were settled in various towns and even rural districts. For a short time these newcomers remained a separate people, but before the twelfth century was over they had become for the most part indistinguishable from the great mass of the English people amongst whom they had come. They had nevertheless made that people stronger, more vigorous, more active-minded, and more varied in their occupations and interests. King William and his successors retained their continental dominions and even extended them after their acquisition of the English kingdom, so that trade between the two sides of the Channel was more natural and easy than before. The strong government of the Norman kings gave protection and encouragement to this commerce, and by keeping down the violence of the nobles favored trade within the country. The English towns had been growing in number, size, and wealth in the years just before the Conquest. The contests of the years immediately following 1066 led to a short period of decay, but very soon increasing trade and handicraft led to still greater progress. London, especially, now made good its position as one of the great cities of Europe, and that preeminence among English towns which it has never since lost. The fishing and seaport towns along the southern and eastern coast also, and even a number of inland towns, came to hold a much more influential place in the nation than they had possessed in the Anglo-Saxon period.