I got a sense of this when I read SPQR by Mary Beard (the woman you may have heard of from a twitter fight with people criticizing a depiction of an African Roman soldier in some cartoon). The book not only goes into what we know about a period of ancient Rome, but how we know what we know about it -- what the actual original sources are and what the archaeology tells us.
The biggest implication of this in the book is that we really know jack shit about Rome prior to maybe the 4th century BC (which I think is the point where Rome Total War campaigns start), but a ton of people parrot stories about the original kings of Rome and the tradition that it was founded in the 7th or 8th century BC as if it's historical fact. Even the Wiki articles on Rome do this.
This has got me thinking about all the history videos I like to watch on YouTube. They usually seem to extensively report their sources though, and those sources are usually thick books on the subjects of each video. They're probably a step above people on some forums.
