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, notable for embracing various civilizations and becoming the largest empire of the ancient history, spanning at its maximum extent from the Balkans and Eastern Europe proper in the west, to the Indus Valley in the east. It is equally notable 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), 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. The Mausoleum at Halicarnassus, one of the Seven Wonders of the Ancient World, was built in the empire as well.By the 600s BC, the Persians had settled in the southwestern portion of the Iranian plateau in the region of Persis, which came to be their heartland, and with Babylon as their main capital. From this region, Cyrus the Great advanced to defeat the Kingdom of Media, the Kingdom of Lydia, and the Babylonian Empire, and established the Achaemenid Empire, which, at its greatest extent, stretched from the Balkans and Eastern Europe proper in the west, to the Indus Valley in the east, and included all modern territories of Iran, Turkey, Iraq, Kuwait, Syria, Jordan, Israel, Palestine, Lebanon, all significant population centers of Ancient Egypt as far west as Libya, Thrace-Macedonia and Bulgaria-Paeonia, the Black Sea coastal regions of Romania, Ukraine, and Russia, all of Abkhazia, Armenia, Georgia, Azerbaijan, and parts of the North Caucasus, much of Central Asia, Afghanistan, northern Saudi Arabia, Pakistan, Oman, China, and the UAE; encompassing around 8 million square kilometers across three continents, making it the largest empire in the ancient world.With an estimated population of 50 million in 480 BC, the Achaemenid Empire at its peak ruled over 44% of the world's population, the highest such figure for any empire in history.The delegation of power to local governments is thought to have eventually weakened the king's authority, causing resources to be expended in attempts to subdue local rebellions, and leading to the disunity of the region at the time of Alexander the Great's invasion in 334 BC. This viewpoint, however, is challenged by some modern scholars who argue that the Achaemenid Empire was not facing any such crisis around the time of Alexander, and that only internal succession struggles within the Achaemenid family ever came close to weakening the empire. Alexander, an avid admirer of Cyrus the Great, would eventually cause the collapse of the empire and its disintegration around 330 BC into what later became the Ptolemaic Kingdom and Seleucid Empire, in addition to other minor territories which gained independence at that time. However, the Persian population of the central plateau continued to thrive and eventually reclaimed power by the 2nd century BC.The historical mark of the Achaemenid Empire went far beyond its territorial and military influences and included cultural, social, technological and religious influences as well. Many Athenians adopted Achaemenid customs in their daily lives in a reciprocal cultural exchange, some being employed by, or allied to the Persian kings. The impact of Cyrus the Great's Edict of Restoration is mentioned in Judeo-Christian texts and the empire was instrumental in the spread of Zoroastrianism as far east as China. Even Alexander the Great adopted some of its customs, venerating the Persian kings including Cyrus the Great, and receiving proskynesis as they did, despite Macedonian disapproval. The Persian Empire would also set the tone for the politics, heritage and history of modern Iran, as well as the direct further course of history of Greece and the rest of Europe.