The Achaemenid Empire (Old Persian) (c. 550–330 B.C.E.), 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. stretched 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, ruled by monarchs, to become the largest the world had yet seen.
Greco-Persian War Wikipedia, the free encyclopedia