What caused the Renaissance of cities in the early Middle Ages?

The revival of cities arose in the Middle Ages due to the fact that people had a surplus in the economy. They sought to exchange or sell them and get benefits from it. Trade took place in the cities, as there was a large crowd of people. Also, the urban population increased due to the fact that these territories were located on trade routes. Gradually, artisans and usurers moved there. Over time, tillage tools and variety in products developed, so it was easier to sell them at the fair.