The main difference between a canal and a river is that a river is a natural flow of water while a canal is man-made. A river by definition flows from inland into the sea while a canal is most often constructed to connect existing rivers, lakes or oceans.
Both rives and canals have been important to human history in many respects. Systems of rivers, canals and inland waterways connect ocean transportation — and, by extension, overseas commerce and communication, — inland from coastal areas.
Since antiquity, civilizations have concentrated along rivers, including the Tigris-Euphrates and Nile river systems. As a natural means of transportation, rivers have also provided a means for travelers, conquerors and colonialists to penetrate land. For example, the St. Lawrence, Mississippi, Missouri, Mohawk and Ohio river systems were the chief means for the first European colonialists to travel through the North American continent.
Ancient Middle Eastern societies like the Phoenicians, Persians and Egyptians built canals for irrigation purposes. Pharaoh Pepi built a series of five canals, the first known to have been built to improve the flow of a river, in 2300 to 2180 B.C.E. The Persian king Xerxes built the first direct sea level canal at the Mount Athos peninsula in 480 B.C.E.