Not many of the tourists who go to see the Crown Jewels in the Tower realise that two of the most magnificent stones are from Afghanistan, the Black Prince’s Ruby and the Timur Ruby. Henry V wore the two-inch-long Black Prince’s Ruby on his helmet at Agincourt. It is now the centrepiece of the Imperial State Crown. The Timur Ruby is even larger and carved with the name of Tamerlane and five of its other keepers. Both almost certainly came from a mine in the Pamirs first described by Marco Polo, in one of the most inaccessible parts of Afghanistan. Gary Bowersox employed old maps and his considerable courage to rediscover it, trekking with horses up the rocky Oxus Valley and across passes christened, by the Danish expedition that first mapped them, Devil’s Pass One, Two and Three.

Too often travel writers confect exquisite experiences out of very little, but Bowersox has, if anything, too much experience to fit easily into a book. He has been travelling in Afghanistan, where he is a well-known figure, for thirty-five years. He served in the US Army during the Vietnam War and is large, tough, generous and unassuming. I first met him in 2001.