What contrubuted to the growth of towns in medieval Europe?

There are no different thing from what contributes to city growth of then and now.

Two things contributed to this which are :

1. The growth of close castles

2. When a city is turned into a commercial hub. That is the growth of market which attracts people from remote countries to the hub where things happens.

They had better agricultural advances - they produce crops, maintain the soil, and raise livestock. They also had use of iron goods - which was very beneficial for trading, spreading ideas, and better knowledge regarding other kinds of agricultural methods.

Hope this helps!