A mysterious engraved slab of smooth marble known as "The Image of Christ" plays an important role in Desert Winds. Devon and the Frenchwoman find both the key to survival and the mystery of Christ's family in the words encrypted on the stone. If you wonder about the family found in the fresco at the end of the book, read Margaret Starbird's Lady with the Alabaster Jar or The Goddess in the Gospels.
This is the fictional "Image of Christ." A polished stone tablet, dating to the time of Christ, contains a simple but powerful message. The tablet is coveted, thrown away, traded, then finally left to rest. The message is understood, then its meaning is lost again before it is found by Granwin.
The tablet bares a simple encryption which could have been decrypted by the Parthian scholars as easily as they decrypted the secret dispatches of the Roman legions under Marcus Licinius Crassus at the Battle of Carrhae, one of many great battles between Rome and Parthia. Ancient Parthia lay between the Caspian Sea and the Persian Gulf, and its boundaries included all of modern Iran and contained portions of what are now modern Iraq, Turkey, Armenia, Azarbaijan, Turkmenistan, Afghanistan and Pakistan. Then and now, a battlefield for morality, cultures, and forever, raw power. As powerful as the message in Brown's Da Vinci Code, the mystery of the Image of Christ is hidden in Behind the Green Water.
A hint - not many of us are Greek scholars, so the underlying text is in modern English. The word scratched above the carved letters is a Greek decryption of one of the words of the text.
Now for the solution: (Caution - proceed only if you want a hint to the ending of the story.)