People have been communicating with symbols since the dawn of man. American Indians carved images into rocks to speak a language of symbols. They were communicating things about their lives like religion, food, tribal happenings.
The word petroglyph has Greek origins that means “rock carving”. Here is an example of a many symbols carved into a sandstone rock face. Over time rock faces get a varnished coating that can be etched into like this one.
This is an interesting site that is a good place to start to learn more about petroglyphs, particularly in North America http://www.crystalinks.com/petroglyphs.html
