The Achaemenid Empire (/əˈkiːmənɪd/ c. 550–330 BC), also called the First Persian Empire, was an empire based in Western Asia, founded by Cyrus the Great. Ranging at its greatest extent from the Balkans and Eastern Europe proper in the west to the Indus Valley in the east, it was larger than any previous empire in history, spanning 5.5 million square kilometers. Incorporating various peoples of different origins and faiths, it is notable for its successful model of a centralised, bureaucratic administration (through satraps under the King of Kings), for building infrastructure such as road systems and a postal system, the use of an official language across its territories, and the development of civil services and a large professional army. The empire's successes inspired similar systems in later empires.