Earlier quoted context omitted.
I am not claiming to know any exact value. But previous comparisons I've seen do it by looking at some good or asset which has remained relatively unchanged since ancient time and then using the modern day price of that good to extrapolate the growth of the economy since then.
I guess it seems clever, but also it seems like it wouldn't make any sense. I mean an obvious comparison would be some of the things on this list http://medieval.ucdavis.edu/120D/Money.html but how does it even work - what things on that list have actually remained unchanged? Is a chicken in medieval times really the same as chicken today, and that's just in the last 800 years, not in the last 5000. And in what direc…
Of course nobody is doing this silly thing, but trying to think about how the way it is being done works seems to be equally as silly to me.