IN HIS NATURAL HISTORY, a first-century A.D. book that purports to contain everything then known about the world, the Roman historian Pliny the Elder briefly describes the Decapolis, a region at the Roman Empire’s eastern edge. He notes that, as its Greek name suggests, the Decapolis consists of 10 cities—among them Damascus, Syria; Philadelphia, now Amman, Jordan; and Hippos, Israel—though he adds that “all writers are not agreed” precisely which cities should make the list. A later account, from the second-century A.D. Greek geographer Ptolemy, who lived in the Roman province of Egypt, jettisons one of Pliny’s Decapolis cities, Raphana, but adds nine more, for a total of 18. One of the additions was a newly founded city with the Latin name of Capitolias.
Many cities of the Decapolis were…