Iran also known as Persia officially the Islamic Republic of Iran is a country in Western Asia. With over 81 million inhabitants, Iran is the world’s 18th-most-populous country. Comprising a land area of 636,372 sq mi. it is the second-largest country in the Middle East and the 17th-largest in the world. Iran is bordered to the northwest by Armenia and the Republic of Azerbaijan, to the north by the Caspian Sea, to the northeast by Turkmenistan, to the east by Afghanistan and Pakistan, to the south by the Persian Gulf and the Gulf of Oman, and to the west by Turkey and Iraq. Iran is home to one of the world’s oldest civilizations, beginning with the formation of the Elamite kingdoms in the fourth millennium BCE. It was first unified by the Iranian Medes in the seventh century BCE, reaching its greatest territorial size in the sixth century BCE, when Cyrus the Great founded the Achaemenid Empire, which stretched from Eastern Europe to the Indus Valley, becoming one of the largest empires in history.