The iron scabbard of a sword. A well-rubbed coin. How old are these things? The running man doesn’t know. “Kadim jidn,” he says: Very old. He shrugs. The Hejaz—a crossroads where Arabia ...

Struck from gold mined at a site owned by the Caliph himself, the coin bears the inscription “Mine of the Commander of the Faithful in the Hejaz”. That makes it the earliest known Islamic coin ...