Today, the top 1% of America controls roughly 40% of the nation's wealth. Historians Walter Schiedel and Steven Friesen examine income inequality in the Roman Empire for comparison:
Different methods of estimating the Gross Domestic Product of the Roman Empire in the second century C.E. produce convergent results that point to total output and consumption equivalent to 50 million tons of wheat or close to 20 billion sesterces per year. It is estimated that élites (around 1.5 per cent of the imperial population) controlled approximately one-fifth of total income, while middling households (perhaps 10 per cent of the population) consumed another fifth. These findings shed new light on the scale of economic inequality and the distribution of demand in the Roman world.
To add some armchair econohistory to the story, though, it seems structurally more difficult to amass wealth in an agrarian, manpower driven society where your work-product is generally literally the sweat of your brow (and where subsidence farming is prevalent).