During the Middle Ages, the once ancient societies of the European continent began to transform into more modern societies as we know today. The rural agricultural societies of previous years began to transform into urban industrial societies. The development of towns became possible with increasing agricultural production which allowed the population to rise due to an increase in food supply. As populations rose, cities expanded their walls in order to harbor the increasing number of people. Cities served as a marketplace where most people produced and vended goods in their own home. Accompanying the growth of cities was the growth of long-distance trade. Merchants began to produce goods not only for local trade but for foreign trade as well.