For countries for which there was data, Piketty collected census and tax data for his book Capital and Ideology and my recollection is the worst inequality in r

For countries for which there was data, Piketty collected census and tax data for his book Capital and Ideology and my recollection is the worst inequality in recorded history was during pre French Revolution times where he measured using I think 10 percent bins for each percentage of a nation's wealth. He put all the data on his website, but I didn't bother looking into it further. But he noted that as a society got wealthier, the higher inequality can rise, because the non elites have enough to for basic survival in a wealthy society, i.e. rising tide lifts all boats but only up to a certain point.