When in 2011 Samuel Arbesman, at that time at the Institute for Quantitative Social Science at Harvard University, analyzed the lifespans of 41 ancient empires that existed between 3000 bce and 600 ce, he found that their mean duration was 220 years, but that the distribution of imperial lifespans was highly skewed, with those empires enduring at least 200 years being roughly six times as common as those surviving for eight centuries.
