three essential services and God had made each one the responsibility of a separate class of people; knights provided protection, clergy interceded with prayer, and peasants and village artisans produced food and supplies. The revival of towns and trade in the eleventh century created a fourth class composed of merchants. Its members were thought of as "middle class". They were economically productive like peasants, but they did not work the land. They had wealth like nobles and clergy, but they were not part of the political power structure. They did not fit neatly into the old social order, and the pressure they exerted.