Question

Why are so many big cities located along the banks of a river

Answer 1

There are many reasons why big cities are located along the banks of a river:

Rivers provide good shipping routes and transportation of both goods and passengers.

Products can be shipped up and down rivers, instead of clogging roadways with trucks.

Answer 2

The cities, especially the largest ones have almost always been located along the banks of a river, usually a larger one. ... In the past, a major reason was the fertile soil, as the larger population needed more food, and the fertile deposits by the rivers enable high scale production of food. ( cite: google )