Shugborough inscription

Look from afar at the 18th-century Shepherd's Monument in Staffordshire, England, and you might take it as nothing more than a sculpted re-creation of Nicolas Poussin's famous painting, “Arcadian Shepherds.” Look closer, though, and you'll notice a curious sequence of letters: DOUOSVAVVM — a code that has eluded decipherment for over 250 years.

Though the identity of the code carver remains a mystery, some have speculated that the code could be a clue left behind by the Knights Templar about the whereabouts of the Holy Grail.

Many of the world's greatest minds have tried to crack the code and failed, including Charles Dickens and Charles Darwin.

Georgia Guidestones

The Georgia Guidestones, sometimes referred to as the "American Stonehenge," is a granite monument erected in Elbert County, Ga., in 1979. The stones are engraved in eight languages — English, Spanish, Swahili, Hindi, Hebrew, Arabic, Chinese and Russian — each relaying 10 "new" commandments for "an Age of Reason." The stones also line up with certain astronomical features.

Though the monument contains no encrypted messages, its purpose and origin remain shrouded in mystery. They were commissioned by a man who has yet to be properly identified, who went by the pseudonym of R.C. Christian.

Of the 10 commandments, the first one is perhaps the most controversial: "Maintain humanity under 500,000,000 in perpetual balance with nature." Many have taken it to be a license to cull the human population down to the specified number, and critics of the stones have called for them to be destroyed. Some conspiracy theorists even believe they may have been designed by a "Luciferian secret society" calling for a new world order.

Rongorongo

Rongorongo is a system of mysterious glyphs discovered written on various artifacts on Easter Island. Many believe they represent a lost system of writing or proto-writing and could be one of just three or four independent inventions of writing in human history.

The glyphs remain undecipherable, and their true messages — which some believe could offer hints about the perplexing collapse of the statue-building Easter Island civilization — may be lost forever.

Go figure

Few stories have the power to captivate us more than those that remain unresolved. Codes, puzzles and cryptic public art tease us with their intrigue: Why is their message coded? What great secrets might they hide? Despite the efforts of our most learned historians, cleverest cryptographers and most determined treasure hunters, history is replete with riddles that continue to confound us today. Fictional tales like those featured in “The Da Vinci Code” and the movie “National Treasure” have got nothing on these real-life puzzles. Here's our list of 10 of the world's most cryptic unsolved mysteries and codes. (Text: Bryan Nelson)

Phaistos Disc

The mystery of the Phaistos Disc is a story that sounds like something out of an Indiana Jones movie. Discovered by Italian archaeologist Luigi Pernier in 1908 in the Minoan palace-site of Phaistos, the disc is made of fired clay and contains mysterious symbols that may represent an unknown form of hieroglyphics. It is believed that it was designed sometime in the second millennium BC.

Some scholars believe that the hieroglyphs resemble symbols of Linear A and Linear B, scripts once used in ancient Crete. The only problem? Linear A also eludes decipherment.

Today the disc remains one of the most famous puzzles of archaeology.