Four Valleys, One Pattern
1The four cases in this gallery come from places thousands of miles apart: the Nile Valley in Egypt, the plain of the Tigris and Euphrates rivers in Mesopotamia, the Indus Valley in what is now Pakistan, and the valley of the Huang He, or Yellow River, in northern China. Between about 3500 and 1500 BCE, some of the world's first cities grew up in each of these valleys. The wall chart beside this panel gives each site's latitude and longitude and the rain it gets in a year today.
2Latitude measures how far a place is north or south of the equator. Longitude measures how far it is east or west of the prime meridian. All four sites lie north of the equator and east of the prime meridian, in a band between about 24° and 34° north. At these latitudes, summers are long and hot, so crops can grow for many months of the year. Rain is another matter. As the chart shows, most of the sites get very little of it.
3In lands this dry, a river was a lifeline. The Nile rose each summer after heavy rains fell in the highlands of East Africa, far upstream. The Indus rose with melting Himalayan snow and summer monsoon rains. Both floods spread water and fresh silt over the fields. The Tigris and Euphrates flooded in spring, when snow melted in the mountains to the north. Their floods were harder to predict, and in some years they came just as the barley was ripening. The Huang He carries so much fine yellow soil, called loess, that the soil gave the river its name.
4Rivers gave more than water. Boats carried grain, stone and other goods along them. People who shared a river had reasons to work together, digging canals to carry water to new fields and building earth banks to hold back floodwater. Rivers could also destroy. A flood that rose too high could wash away a village, and one that stayed too low could mean a poor harvest and hunger. The objects in this gallery show some of the ways people learned to live with their rivers.