Standard of the Achaemenid Empire, 559–529 BC,Iran Aufkleber

The Achaemenid Empire or Achaemenian Empire, also known as the Persian Empire or First Persian Empire (/əˈkiːmənɪd/; Old Persian: 𐎧𐏁𐏂, Xšāça, lit. 'The Empire' or 'The Kingdom'), was an Iranian empire founded by Cyrus the Great of the Achaemenid dynasty in 550 BC. Based in modern-day Iran, it was the largest empire by that point in history, spanning a total of 5.5 million square kilometres (2.1 million square miles). The empire spanned from the Balkans and Egypt in the west, most of West Asia, the majority of Central Asia to the northeast, and the Indus Valley of South Asia to the southeast. Around the 7th century BC, the region of Persis in the southwestern portion of the Iranian plateau was settled by the Persians. From Persis, Cyrus rose and defeated the Median Empire as well as Lydia and the Neo-Babylonian Empire, marking the establishment of a new imperial polity under the Achaemenid dynasty. In the modern era, the Achaemenid Empire has been recognised for its imposition of a successful model of centralised bureaucratic administration, its multicultural policy, building complex infrastructure such as road systems and an organised postal system, the use of official languages across its territories, and the development of civil services, including its possession of a large, professional army. Its advancements inspired the implementation of similar styles of governance by a variety of later empires. By 330 BC, the Achaemenid Empire was conquered by Alexander the Great, an ardent admirer of Cyrus; the conquest marked a key achievement in the then-ongoing campaign of his Macedonian Empire. Alexander's death marks the beginning of the Hellenistic period, when most of the fallen Achaemenid Empire's territory came under the rule of the Ptolemaic Kingdom and the Seleucid Empire, both of which had emerged as successors to the Macedonian Empire following the Partition of Triparadisus in 321 BC. Hellenistic rule remained in place for almost a century before the Iranian elites of the central plateau reclaimed power under the Parthian Empire.