The Persian Empire in Antiquity was the largest geographical empire in its time, at its height stretching from India all the way into southern Europe and down to Egypt, primarily under Cyrus the Great. It had two capitals: Susa and Persepolis. The Persian Empire came into being in 539 B.C. with the defeat of the Babylonian Empire, it continued until it was conquered and largely absorbed by Alexander the Great in 330 B.C. The Persian Empire and several of its rulers are discussed in the Bible in the book of Daniel and Esther.
A later Persian Empire re-emerged in the later period of the Roman Empire and outlived the Western Roman Empire. After a devastating war with the Byzantine Empire that left both sides severely drained, Islam came on the scene from Saudi Arabia and completely conquered the Persian Empire in a quick campaign that ended in 651 A.D.