In an age of thrillers and mystic secrets, here is a true-life Da Vinci Code: the Sator Enigma, from ancient Rome. Is it Christian? Is it Pagan? What did it mean to the Romans? Should it mean anything to us in modern times? For centuries, scholars have been baffled by a mysterious inscription found in ruins across the Roman Empire: at a military headquarters in Syria, a sport complex in Pompeii, two British colonial towns... it must have...