We can see the city of Cologne in the middle of the Middle Ages, the rapid development of the commodity economy, the expansion and renovation of the city walls, the gradual increase in the population of the city, and the growth of the citizen class, further boosted the expansion of the city.
Option C: Prosperity in commerce boosts the growth of the citizen class.
Cologne is also the fourth largest city in Germany today, the largest city in North Rhine-Westphalia, the economic, cultural and scientific and educational center of the Rhine region, the most famous Cologne in the Middle Ages is the Cologne Cathedral, which was built in 1248, and the altar cross is the classic of the classics, and is the oldest and most famous treasure in the large sculpture in Europe.
Cologne's earliest history can be traced back to the 1st century BC, when the Roman Empire was at its peak, and the barbarian Germans in the north often looked across the Rhine River, gradually evolving into a military fortress and becoming the latest frontier next to the Rhine. The Middle Ages was the heyday of Cologne, Charlemagne once used Cologne as the residence of the archbishop, and it was the largest city in Germany at that time.
Today's Cologne is not only a church, but also a famous exhibition city, the specialty is flower water, Cologne water, in Cologne, perfume, toilet water specialty stores everywhere, on both sides of the street, people come and go, lively and extraordinary.