The data in the graph was taken from the lowest estimates in this Census Bureau compilation.
As you can see, the lowest estimators, McEvedy and Jones, simply did not provide an estimate for 400 BC; hence that year shows as anomalously high.
The data in the graph was taken from the lowest estimates in this Census Bureau compilation.
As you can see, the lowest estimators, McEvedy and Jones, simply did not provide an estimate for 400 BC; hence that year shows as anomalously high.