Here's a fun thing to think about: There might have been Native American city founded in 800 BC or so that became a mighty Rome-style empire that ruled modern-day Virginia for a thousand glorious years before collapsing to barbarians in 200 AD, leaving gorgeous ruins that lasted for another 1000 years or so before the elements and looters finally reduced it all to nothing.

There's no evidence for this. I made it up. But there wouldn't be any evidence if it happened. All the physical evidence would have been gone hundreds of years before Columbus arrived, and 90% of the native population who'd know stories about it were wiped out before Europeans felt like interviewing them about ancient history, so they took that knowledge to their graves.