Click on the colored circles in the map key. In 1850 northwestern Europe had the greatest number of large cities (cities with a population of at least 100,000 inhabitants). Looking at the map and taking in to consideration your knowledge of the time, what is the main reason for this urban density?

The map shows several large cities that are along two of Europe’s major rivers, one which empties into the North Sea, and the other which empties into the Black Sea. Which rivers are they?