An ancient secret is enshrined in a mysterious inscription dated 1207, still to be seen on the ornate marble floor of the Basilica of San Miniato in Florence. This story holds the key to that secret. The narrative unfolds in the latter part of the 12th century when Frederick Barbarossa, the Holy Roman Emperor, was forcefully seeking to bring the Italian communes to heel under his rule in Europe, and the Latin Kingdom of Jerusalem was reeling under...