Nile
The world's longest river, lifeblood of ancient Egypt
For more than four thousand miles the Nile pushes north across the Sahara, a thread of green water cutting through some of the most arid country on Earth. It is the only major river to flow from the tropics into the Mediterranean, gathering snow-fed and rain-fed waters from the Ethiopian highlands and the great lakes of East Africa before threading the Egyptian desert. Without it, the eastern Sahara would be empty sand. With it, one of humanity's first civilizations took root along its banks.
The river is really two great systems joined at Khartoum. The White Nile, draining the equatorial lakes and the vast Sudd wetland, supplies a steady year-round flow. The Blue Nile, born in the Ethiopian highlands at Lake Tana, contributes the summer monsoon torrent that once flooded Egypt every August and laid down the black silt that made the valley fertile. The Atbara adds a final seasonal pulse. Below Aswan the combined river runs unbroken to a broad delta where it splinters into distributaries and reaches the Mediterranean Sea.
Egyptian life was organized around the river's rhythm: the inundation, the planting, the harvest, the calendar itself. Temples, pyramids and cities clustered along its banks because almost nothing grew beyond them. In the twentieth century the Aswan High Dam ended the annual flood, trading silt and sardines for reliable irrigation and electricity. Today the Nile is shared, and disputed, among eleven nations — Ethiopia's Grand Renaissance Dam on the Blue Nile has sharpened a long argument over who controls the water that hundreds of millions of people depend on.