We do not adequate records to get closer than a rough conservative estimate of about 40 million.
At its peak, the estimated population of the Persian Empire was around 50 million people.
There are many guesses as we have no record. Perhaps 40 million.
The Persian Empire.
The Persian Empire was not a person.
Persian Empire
The Persian Empire absorbed the Babylonian Empire.
Alexander the Great defeated the Persian empire
The Persian Empire absorbed the Baabylonian Empire.
Alexander conquered the Persian Empire.
An empire is an empire, a war is a war.
The Persian Empire incorporated the Indus Valley.
They turned the alliance of cities against the Persian Empire into an empire of their own and used the financial contributions of the cities to beautify Athens and keep half its population on the public payroll.