More than a thousand years after a ship vanished off the coast of modern-day Croatia, archaeologists have uncovered a wreck that might reshape our ideas of the medieval world.

National Geographic archaeologist George E. Stuart reported in 1975 on the scientists who sought to decode the ancient language—and the looters who stood in their way.

Murujuga, also known by the modern name Burrup Peninsula, in northwestern Australia, is home to potentially the world’s oldest and most endangered petroglyphs. Some of the more than one million images ...