I think "made up" is fair. I can't know what his process was and everybody makes mistakes, but almost every single thing he said about history was wrong in a way that was convenient to his narrative, and it's not like he ever retracted anything. Surely if he wrote a whole book about dealing with bullshit he could have used that opportunity for some reflection about his past mistakes, now that would have been interesting to read.

Do you have a specific source for this claim? I have read through what someone else posted in this thread (https://talesoftimesforgotten.com/2020/02/05/carl-sagan-was-...) and while some details are indeed incorrect, a lot of it is nitpicking or common misconceptions from his time.

You think it's nitpicking because you don't care much about truth when it comes to history, and that's perfectly fine. But it's weird to complain about other people's baloney while spreading your own, and I think in his position as a trusted science communicator he should have been more responsible about this stuff.

No, I think it's nitpicking because it truly is in some cases. Science communication is about simplifying things and making shortcuts while keeping things engaging. Of course Sagan didn't go into a tangent about the first use of the word barbarians or whether ancient greeks would define robots the same way we do. That's pedantic.

There are a few good examples of significant errors in the link I cited which I think are substantial - the portrayal of Hypatia is a big one. I just wondered whether there were more discussions about other history topics he got wrong, since you yourself mentioned that "almost every single thing" he said was wrong.