West Africa's greatest river, which rises near the Atlantic, runs the wrong way into the Sahel toward the desert's edge, and finally reaches the sea in a delta whose oil has made it one of the most fought-over and polluted places on Earth.
The Niger rises within sight of the Atlantic and then flows the wrong way, looping northeast into the desert before it bends back to the sea. That backward arc watered some of the great cities and later empires of the Sahel and baffled outsiders for centuries. Its delta now holds the bitter modern parable of oil wealth that poisons the people who live on top of it.