Deutsche Bank released a note that included a chart of major global economies in the first year of the common era.
They're ranked by "economic power," which is measured in terms of economic output compared to the total world output.
Unsurprisingly, Augustus' Roman Empire ranked first. It controlled slightly over 25% of total world output. Rome's largest competitors, Parthia (whose modern territory is roughly modern day Iran) and Germany controlled only 2% and 1%, respectively, of the global economic output.
Deutsche Bank's note added that, "whilst economic output is not the only important variable in understanding the ability of a nation or empire to exert global power, it is probably the most important basic element as it determines the total pool of resources that can be devoted to war."
Deutsche Bank
"Here the 'world' is defined as the empire's contemporaries would have thought of it - as Western Europe, North Africa and the Middle East," noted Reid.
As you can see from the chart, certain empires such as China under the Han Dynasty are excluded.