Watersheds have a geological history. Rivers change the landscape through which they pass; those changes in turn change the river. It is important to understand the historical development of watersheds. Human history is also often enacted along river courses and in watersheds. Rivers are the sites of many important human settlements. Rivers are the reason why agriculture develops in some areas and not in others. Rivers are often important trade and travel routes. The study of rivers is rich in history whether on the time scale of geological processes or more recent human history.