The Achaemenid Empire ( ə-KEE-mə-nid; Old Persian: 𐎧𐏁𐏂, Xšāça, lit. 'The Empire' or 'The Kingdom') was an ancient Iranian empire founded by Cyrus the Great of the Achaemenid dynasty in 550 BC. At peak, its territorial extent was roughly 5.5 million square kilometres (2.1 million square miles), making it the largest empire of its time. Based in the Iranian plateau, it stretched from the Balkans and Cyrenaica in the west to the Indus Valley in the east, including Anatolia, Cyprus, Mesopotamia, the Levant, the South Caucasus, parts of Eastern Arabia, and large parts of Central Asia. By the 7th century BC, the region of Persis, located in the southwestern part of the Iranian plateau, had been settled by Persian people. From Persis, Cyrus rose and defeated Media, Lydia, and the Neo-Babylonian Empire, thus marking the establishment of a new imperial polity in the ancient Near East. While its conquests were largely successful in most regions, the Achaemenid Empire's attempts to expand into Greece proved extremely difficult over the course of decades of wars and multiple kings, ultimately resulting in its defeat in the Greek mainland. In 330 BC, amidst a Greek military campaign that began in 336 BC, the Achaemenid Empire was conquered in its entirety by Alexander the Great, who annexed it to his Macedonian Empire. Upon Alexander's death, which sparked the beginning of the Hellenistic period in 323 BC, the majority of the former Achaemenid Empire's territories came under the rule of the Seleucid Empire and the Ptolemaic Kingdom. Almost a century later, Iranian elites in the central plateau successfully reclaimed power from the Seleucids and established the Parthian Empire, which existed for nearly half a millennium before being succeeded by the Iranian Sasanian Empire. In the modern era, the Achaemenid Empire has been recognized for its centralized bureaucracy and administration; its multicultural policy and religious tolerance, especially under Cyrus; its complex infrastructure projects, such as the Royal Road and an organized postal system; the use of official languages (Persian and Aramaic) across its territories; and the development of a civil service and a large, professional army and navy.