Why did medieval towns grow?

Answer 1

Some towns were founded as independent communities. Venice is an example that was a republic from its beginnings. Venice functioned as a part of the Byzantine Empire for a long time, with local independence, but eventually it became fully independent and functioned as a sovereign state.

In some towns, the craftsmen or merchants formed guilds that organized the economic life of the community. These took more and more power from the nobility, because the nobility did not spend much time addressing the economic well being of communities, which became more and more important with the passing of time. The guilds eventually established Medieval Communes (probably commonwealths would be a better word), and these established republican governments or governing bodies in the towns. Some of these towns and cities became free cities in the Holy Roman Empire, and others became fully independent.

There is a link below to an article on medieval communes.
The growth of trade and urbanization created by the Enclosure Movement ended Feudalism at the end of the Middle Ages and beginning of the Renaissance. The newly developing towns and cities no longer needed to depend on a vassal and his knights for protection. With tenant farmers moving to the cities to compete for jobs, unemployment was high. The king hired many of these unemployed workers to serve in the king's army. The cities were free to elect their own local government as a result.

Answer 2

Pre-industrial towns and cities generally grew around transportation routes like rivers, bays, or Roman roads, or near resources like copper or salt mines.

The modern-day equivalent is freeway intersections.