In 1849 Heinrich Barth joined a small British expedition into unexplored regions of Islamic North and Central Africa. One by one his companions died, but he carried on alone, eventually reaching the fabled city of gold, Timbuktu. His five-and-a-half-year, 10,000-mile adventure ranks among the greatest journeys in the annals of exploration, and his discoveries are considered indispensable by modern scholars of Africa. Yet because of shifting politics,...