In which areas of medieval Europe were the richest and most powerful cities? How can this be explained?

The number of rich cities depended on the period of the Middle Ages.

In the early Middle Ages, there were many such cities on the territory of Byzantium (Eastern Roman Empire), for example, Thessalonians or Ravenna and Constantinople itself, as well as Nicea, Alexandria, Syracuse.

In the mature Middle Ages, rich cities were, as a rule, in southern Europe, these are the commercial Italian republics of Genoa and Venice, as well as Pisa at one time. Well, neighboring with them: Bologna, Padua, Verona, Milan. And in northern Europe, the richest cities were the Hansa cities: from London to Novgorod the Great (in the XII-XV centuries, probably the richest city in Russia).

In the 16th century, the rich cities included those that were associated with great geographical discoveries: Seville and Lisbon, as well as cities in the Netherlands, where the first bourgeois revolution took place at the end of the 16th century. Among them: The Hague, Amsterdam, Bruges, Antwerp.