Tehran is the capital of Iran and Tehran Province. With a population of around 9 million in the city and 16 million in the wider metropolitan area, Tehran is the most populous city of Iran, the 2nd-most populous city in Western Asia and the 3rd-largest metropolitan area in the Middle East. It is ranked 29th in the world by the population of its metropolitan area.
In the Classical era, part of the present-day city of Tehran was occupied by a Median city that in the Avesta occurs as Rhaga. It was destroyed by the Mongols in the early 13th century, and remains now as a city in Tehran Province, located towards the southern end of the modern-day city of Tehran.
Tehran was first chosen as the capital of Iran by Agha Mohammad Khan of the Qajar dynasty in 1796, in order to remain within close reach of Iran's territories in the Caucasus, before being separated from Iran as a result of the Russo-Persian Wars,
and to avoid the vying factions of the previously ruling Iranian
dynasties. The capital has been moved several times throughout the
history, and Tehran is the 32nd national capital of Iran.
The city was the seat of the Qajars and Pahlavis, the two last imperial dynasties of Iran. It is home to many historical collections, such as the royal complexes of Golestan, Sa'dabad, and Niavaran, as well as the country's most important governmental buildings of the modern period.
Large scale demolition and rebuilding began in the 1920s, and Tehran
has been a destination for the mass migrations from all over Iran since
the 20th century.
The most famous landmarks of the city include the Azadi Tower, a memorial built during the Pahlavi period, and the Milad Tower, the world's 17th tallest freestanding structure, which was built in 2007. Tabiat Bridge, which was completed in 2014, is considered the third contemporary symbol of the city.
The majority of the people of Tehran are Persian-speaking people, and roughly 99% of the population understand and speak Persian; but there are also large populations of other Iranian ethnicities in the city such as Azerbaijanis, Armenians, Lurs, and Kurds who speak Persian as their second language.
Tehran is served by the Mehrabad and Khomeini international airports, a central railway station, the rapid transit rail system of the Tehran Metro, as well as a trolleybus and a BRT system, and has a large network of highways.
There have been plans to relocate Iran's capital from Tehran to another area; due mainly to air pollution
and the city's exposure to earthquakes. To date, no definitive plans
have been approved. A 2016 survey of 230 cities by consultant Mercer ranked Tehran 203rd for quality of living. According to the Global Destinations Cities Index in 2016, Tehran is among the top ten fastest growing destinations.