What contributed to the growth of towns in medieval europe

It was most likely because of the increase of trade. It could also be because of the growing popularity which attracted travelers, visitors, nosy people, etc., which of course made them have to expand the places the travelers had to stay like motels and whatever else including houses if they decide to stay. Hope that helped

Probably another good cause was religion. Islamic religion swept through during the arabian empire rising. They took control of jerusalem the christ town. Because of this they also swept through syria egypt and palestine. This caused a holy war. Their were near 1.6 billion muslims at that time.