The Achaemenid Empire, or "Achaemenid Persian Empire", (550–330 BC) was the first of the Persian Empires to rule over significant portions of Greater Persia (or Iran). It followed the Median Empire as the second great empire of the Iranian peoples. At the height of its power, the Achaemenid Empire had about 7.5 million square kilometers and was territorially the largest empire of classical antiquity.