I first read about Jasper Evans in a book by the explorer John Hare called Shadows Across the Sahara. Hare set out to retrace an ancient trade route from Lake Chad to Tripoli, a three month south-to-north crossing of the Sahara — 1,462 miles of barren desert known in the days of slavery as a place strewn with the carcasses of men and camels. The route was last crossed by Hanns...