It wasn’t always a desert. The Saharan plain was once open grassland with occasional forests. As late as the time of Julius Caesar, and even afterwards, Romans reported elephants, leopards and lions on the North African shores – along with abundant timber. But like that timber, which was cut down by the Carthaginians and Romans to build their navies, little remains of the Saharan plant life today.
The changes began around three and a half thousand years earlier, with a combination of changes in prevailing winds, a shift in the planet’s orbit and increased cultivation of the land – at this time, for example, south western Egypt and the Sudan were great agricultural realms, for example. But within a few hundred years, the region had become almost impassible, with few other than the Berbers prepared to cross the region until the invention of modern cooling systems in the Twentieth Century.