13 historic monuments, puzzles which are still not solved

8. The stone balls of Costa Rica

Prehistoric petroglyphs along the Pacific coast nearly fell victim to vandalism. The workers who discovered them were convinced they concealed hidden gold.

Unfortunately, the artifacts still endured damage as efforts to attract tourists led to their placement in urban areas. The constant movement of these relics has made precise dating impossible. The theory that they originated from water has been discredited.

Ultimately, what are these markings about? Are they symbols of planets or boundary signs? The theories abound, but evidence is sorely lacking.