The Achaemenid Empire (Persian: امپراتوری هخامنشی) (c. 550–330 B.C.E.), also known as the Persian Empire, was the successor state of the Median Empire, expanding to eventually rule over significant portions of the ancient world which at around 500 B.C.E., streched from the Indus Valley in the east, to Thrace and Macedon on the northeastern border of Greece. The Achaemenid Empire would eventually control Egypt, encompassing some 1 million square miles unified by a complex network of roads, and ruled by absolute monarchs to become the greatest empire the world had ever seen.
The Persians originally were nomadic, pastoral people in the western Iranian plateau and by 850 B.C.E. were calling themselves the Parsa and their constantly shifting territory Parsua. For the most part the early Persians had settled in the southwest Iranian plateau, bounded on the west by Tigris river and on the south by Persian Gulf which had become their heartland for the duration of the Achaemenid Empire. It was from this region that eventually Cyrus the Great (Cyrus II of Persia) would advance to defeat the Median, the Lydian, and the Babylonian Empires, opening the way for subsequent conquests into Egypt and Asia minor.