Who had more money, John D. Rockefeller or Genghis Khan? Its a simple question with a very difficult answer.

This ranking of the richest people of all time is based on hours of interviews with academic economists and historians. To read more about how the order was determined despite the difficulty of comparing wealth across a wide range of time periods and economic systems,read this.

But for now, suffice to say that the following is a rigorous but highly debatable attempt to list the wealthiest historical figures in order of their economic influence.

Mansa Musa, the king of Timbuktu, isoftenreferred to as the wealthiest person in history. According to Ferrum College history professor Richard Smith, Musas west African kingdom was likely the largest producer of gold in the worldat a time which gold was in especially high demand.

Just how rich was Musa? Theres really no way to put an accurate number on his wealth. Records are scarce, if non-existent, and contemporary sources describe the kings riches in terms that are impossible for the time.

Some tales of his famous pilgrimage to Meccaduring which Musas spending was so lavish that it caused a currency crisis in Egyptmention dozens of camels each carrying hundreds of pounds of gold. (Smith says one year of Malian gold production probably generated about a ton.) Others said Musas army consisted of 200,000 men, including 40,000 archerstroop numbers even modern superpowers would have a difficult time bringing to the field.

But to get caught up in the kings exact wealth is to miss the point. As Rudolph Ware, an associate professor of history at the University of Michigan, explains, Musas riches were so immense that people struggled to describe them.

This is the richest guy anyone has ever seen, thats the point, says Ware. Theyre trying to find words to explain that. There are pictures of him holding a scepter of gold on a throne of gold holding a cup of gold with a golden crown on his head. Imagine as much gold as you think a human being could possess and double it, thats what all the accounts are trying to communicate.

When no one can even comprehend your wealth, that means youre pretty darned rich.

Not only was Augustus Caesar in charge of an empire that accounted for25% to 30% of the worlds economic output, but according to Stanford history professor Ian Morris, Augustus at one point held personal wealth equivalent to one-fifth of his empires economy. That fortune would be the equivalent of about $4.6 trillion in 2014. For a while, Morris adds, Augustus personally owned all of Egypt. Thats hard to top.

Wealth:Ruled empire with 25% to 30% of global GDP

Chinas Song Dynasty (960 1279) was one of the most economically powerful empires of all time. According to Prof. Ronald A. Edwards, a Chinese economic historian of the Song Dynasty at Tamkang University, the nation accounted forbetween 25% and 30%of the worlds economic output during its peak.

The empires wealth came from both its technological innovations and extreme skill at tax collection, which Edwards says was hundreds of years ahead of European governments. The professor also noted the Song Dynastys government was highly centralized, meaning the emperor held enormous control over the economy.

The greatest emperor of Indias Mughal dynasty, Akbar controlled an empire that accounted for aboutone-fourth of global economic output.Fortunes Chris Matthews cites the late economic historian Angus Maddison, who speculates Indias GDP per capita under Akbar was comparable to Elizabethan England, but with a ruling class whose extravagant lifestyle surpassed that of the European society.

That assertion that Indias elite class was wealthier than their counterparts to the west is backed up by data from economist Branko Milanovic, whoseresearchshows the Mughal Dynasty was one of the most effective empires of all time at extracting wealth from the population.

Wealth:Complete control of a nation with 9.6% of global GDP

Stalin is an uncommon figure in modern economic history: a dictator with absolute power who also controlled one of the largest economies in the world. While it is virtually impossible to separate Stalins wealth from the wealth of the Soviet Union, his unique combination of economic might and complete control of the USSR lead multiple economists to nominate him as one of the richest people of all time.

You can easily see their logic. Data from theOECDshows that in 1950, three years before Stalins death, the USSR made up roughly 9.5% of global economic output. As of 2014, that level of production would be equivalent to nearly $7.5trilliondollars.

While that money didnt belong directly to Stalin, he had the ability to leverage Soviet economic might for any reason he chose.

He had enormous power, and through his power he could have anything he wanted, says George O. Liber, a professor of history at the University of Alabama at Birmingham. He controlled 1/6th of the land surface of the planet without any checks or balances.

Does that make Stalin rich in the traditional sense? Liber isnt so sure. Was he among the wealthiest men? the professor wonders. I suppose if you want to stretch the definition of wealth, but it was not his wealth. He controlled the wealth of the country.

Even so, its hard not to include Stalin on a list of the most economically powerful people in history. His wealth might be uncertain, but theres no question the premiers personal economic influence is unrivaled in recent history.

Rockefeller gets all the press, but Andrew Carnegie may be the richest American of all time. The Scottish immigrant sold his company, U.S. Steel, to J.P. Morgan for $480 million in 1901. That sum equates to about slightly over 2.1% of U.S. GDP at the time, giving Carnegie economic power equivalent to $372 billion in 2014.

Rockefeller began investing in the petroleum industry in 1863 and by 1880 his Standard Oil company controlled90% of American oil production.

According to hisNew YorkTimesobituary, Rockefeller was valued at about $1.5 billion based on a 1918 federal income tax return and estimates of his overall fortunethe equivalent of almost 2% of U.S. economic output that year according to data compiled by MeasuringWorth (the U.S. did not keep official records on national incomeuntil 1932).

The same economic share in 2014 would be equivalent to $341 billion.

The nephew of William the Conqueror, Rufus joined his uncle in the Norman conquest. He died with 11,000, according to Philip Beresford and Bill Rubinstein, authors ofThe Richest of the Rich, which they sayamounted to 7% of Englands GDP at the time. That would amount to $194 billion in 2014 dollars.

As the richest living person, Bill Gates wealth is refreshingly easy to determine. As of this year,Forbesestimatesthe Microsoft founders net worth at $78.9 billion. Thats about $8 billion more than Zara co-founderAmancio Ortega, the second-richest person in the world.

Genghis Khan is undoubtedly one of the most successful military leaders of all time. As leader of the Mongol Empire, which at its height stretched from China to Europe, he controlled the largest contiguous empire in history. However, despite his great power, scholars say Genghis never hoarded his wealth. On the contrary, the Khans generosity was key to his influence.

One of the basis of his success is sharing the spoils with his soldiers and other commanders, says Morris Rossabi, a distinguished professor of history at CUNYs Queens College.

Jack Weatherford, author ofGenghis Khan and the Making of the Modern World, explains that Mongol soldiers, unlike many pre-modern armies, were banned from taking personal loot. After an area was conquered, every item taken was inventoried by official clerks and then later distributed amongst the military and their families.

Genghis still received a share of the spoils, but that hardly made him rich. He built no palace for himself or family, no temple, no tomb, and not even a house, says Weatherford. He was born in a wool ger [yurt] and he died in a wool ger. At death he was wrapped in felt, like any common person, and then buried.

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