Following the overthrow of the Medes by the Persians, they would inherit the former's territories but significantly expand it. Eventually, this First Persian Empire (also better known as the Achaemenid Empire) would stretch three continents, namely Europe, Asia and Africa, encompassing 8 million square kilometers,[2] and be the first world empire and the largest empire the world had yet seen in the ancient world.[3] At its peak it would stretch from Macedon and Paeonia-Bulgaria in the west, to the Indus Valley in the far east. Founded by Cyrus the Great, it was notable for embracing various civilizations and becoming the largest empire of the ancient history, for its successful model of a centralised, bureaucratic administration (through satraps under a king) and a government working to the profit of its subjects, for building infrastructure such as a postal system and road systems and the use of an official language across its territories and a large professional army and civil services (inspiring similar systems in later empires),[4] and for emancipation of slaves including the Jewish exiles in Babylon, and is noted in Western history as the antagonist of the Greek city states during the Greco-Persian Wars.