The Persian Empire in Antiquity was the largest geographical empire ever seen until that time, at its height stretching from India all the way into southern Europe and down to Egypt -- primarily under Cyrus the Great. Coming 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 only a few short years and completed by 330 B.C. The Persian Empire and several of its rulers are discussed in the Bible both in the book of Daniel and the book of Ester.
A later Persian Empire re-emerged in the later period of the Roman Empire and outlived the Western Roman Empire. After a devasting war with the Byzantine Empire that left both sides severly 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.