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Iran is home to one of the world's oldest civilizations, beginning with the formation of the Proto-Elamite and Elamite kingdom in 3200 – 2800 BCE. The Iranian Medes unified the country into the first of many empires in 625 BCE, after which it became the dominant cultural and political power in the region. Iran reached the pinnacle of its power during the Achaemenid Empire founded by Cyrus the Great in 550 BCE, which at its greatest extent comprised major portions of the ancient world, stretching from the Indus Valley in the east, to Thrace and Macedon on the northeastern border of Greece, making it the largest empire the world had yet seen.
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Tehran is the capital of Iran and Tehran Province. With a population of around 8.3 million and surpassing 14 million in the wider metropolitan area, Tehran is Iran's largest city and urban area, and the largest city in Western Asia.
In the 20th and 21st centuries, Tehran has been the subject of mass migration of people from all around Iran. The city is home to many historic mosques, churches, synagogues and Zoroastrian fire temples. However, modern structures, notably Azadi (Freedom) Tower and the Milad Tower, have come to symbolise the city. Tehran is ranked 29th in the world by the population of its metropolitan area. Throughout Iran's history, the capital has been moved many times, and Tehran is the 32nd national capital of Iran although it has been Iran's capital for about 220 years. Although a variety of unofficial languages are spoken, roughly 99% of the population understand and speak Persian.