Just because something old is found, doesn't mean it was dropped there at that time. You can go to just about any coin shop and find Roman coins, therefor, there's also lots of coin collectors out there with Roman coins in their collection. I've found ancient coins in the grass of a modern park and a local school. The park has had coin shows in it.....a kid probably brought an old coin to school for show and tell, and lost it. It's not hard to believe that pre-Columbian coins can be found just about anywhere people have traveled. That 4 dinero coin found in the field could have been dropped there 50 years ago by a worker, or a kid playing or crossing that field. I know several people who keep an old "lucky" coin in their pocket at all times. All it takes is a hole in that pocket and the coin is out for us to find.