What was the revival of Western European cities in the Middle Ages?

After the fall of the Western Roman Empire, ancient European cities were in ruins in the war. Around 10 century, medieval western European cities such as Venice, Genoa, Florence, Milan, Hamburg and Bremen rose. These cities were naturally formed at some crossroads, commercial markets and old city ruins, which constituted the economic center of medieval Western Europe. The rise and prosperity of cities stimulated the greed of feudal lords in western Europe. They regard the city as the source of wealth and exploit it wantonly. In order to win autonomy, the city waged a fierce struggle with feudal landlords. The rise of western European cities in the Middle Ages is of great historical significance. Economically, cities are relatively concentrated in handicrafts and commerce, and their commodity economy has a certain disintegration effect on the feudal economy in Western Europe. Politically, cities, especially those with autonomy, have become a paradise of freedom. The serfs on the farm can obtain their free status as long as they live in a free city for one year and one day. Therefore, there was a proverb at that time: "The air in the city makes people free." The city also formed an alliance with the king to fight against feudal big noble, which accelerated the unification of the country. Culturally, the city has become the cradle of secular culture, various universities have been established in the city, and urban literature reflecting the citizens' mentality has gradually emerged, laying the foundation for the emergence of the Renaissance.