Why did towns grow during the middle ages?

There are a number of reasons why towns grew during the Middle Ages.

One was an increase in trade, and with it an increase in the numbers and prosperity of the mercantile class.

Another was an increase in agricultural efficiency, which made it easier for a farmer to produce a crop, created a surplus of food, and made it possible for a greater part of the population to be doing non agricultural work.

The increase in trade and pilgrimages both made better roads desirable, which made crossroads good places for markets. People travelled more.

The growth of towns fueled itself by supplying an increasingly large group of tradesmen and craftsmen.