Medieval towns grew due to a combination of factors including an increase in trade, European geography, enhanced farming technology and population growth. The Crusades during the 11th century opened up the trading routes across the Mediterranean Sea, while land trade routes from northern Italy to central Europe were also revived. Advances in civil technology allowed towns to support an increasingly concentrated population.
The increased flow of goods into Europe meant that small towns that were situated along trade routes became important centers of commerce. As sea-based trade routes between the East and West were discovered, such as the Straight of Gibraltar, rivers and streams that connected the sea to central Europe became highways of trade as well. Towns sprang up along these waterways and were sustained by the increased trade.
Enhanced farming technologies including the heavy plow made it easier to convert and sustain large areas of farmland. Farming practices like crop rotation and the cultivation of crops such as beans and peas kept farmland fertile and more productive for longer periods of time. This allowed small towns to grow and sustain larger populations.
The population in Europe tripled between 1066 and 1350, largely because of these factors. This, in turn, further sped the growth of medieval towns as increasing numbers of people accumulated in settled areas.