In 550 BCE under King Cyrus the Great when he amalgamated Persia and Media and used the combined strength to take over the Babylonian Empire.
It was begun by Persian King Cyrus the Great from 550 BCE, and taken over by the Macedonian King Alexander the Great from 331 BCE.
To produce a civilisation, after producing a surplus to finance it, you need sophisticated ways of doing things. So you need specialised workers to carry it out. This was begun in the Middle East by the Assyrian Empire, replaced by the Babylonian Empire then by the Persian Empire to carry it on and improve it.
Greco-Persian conflict lasted from 499 to 449 BCE. The contact had begun 50 years earlier, and afterwards lasted until Alexander the Great took over the Persian Empire 334-324 BCE.
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.
The Persian Empire incorporated the Indus Valley.
Alexander conquered the Persian Empire.
An empire is an empire, a war is a war.