The rapids not only provided a source of power in the days before the steam engine but also prevented ocean going ships from venturing farther upstream. It was convenient for people to ship agricultural products and minerals down the James on batteau. Upon reaching Richmond, these raw materials would be unloaded, processed (using the river power) into finished goods, and placed aboard ocean going ships. Tredegar Iron Works milled iron ore into iron, but Richmond's strength was its flour mills. It was often called the flour milling capital of the world. Even though the upper midwest soon proved a better source of iron ore than did western VA and the steam engine became a more convenient power source than the river, Tredegar remained operational until 1951. The huge flour mills all burned during the riots at the end of the Civil War and were never rebuilt.