Tehran is the latest and the largest capital city in the 7000-year history of Persia , as Iran was called by many people in the West before 1935. The original settlement of Tehran , north of the ancient city of Rey , may have been founded as early as the 4th century. By the early 13th century it was a small village. In 1221 invading Mongols led by Chengis Khan destroyed Rey , but Tehran survived and grew slowly in the following centuries. During the reign of the Safavid Shah Tahmasp (1524-1576) a wall and four watchtowers were built around the city , and by the early 17th century Tehran had about 3000 houses. In the 1720s Afghan invaders attacked Tehran. The town defeated the initial Afghan force but fell to the main Afghan army and suffered tremendously under their occupation from 1723 to 1729. Nadir Shah freed Tehran in 1729. In 1788 Aqa Mohammad Khan , founder of the Qajar dynasty , made Tehran his capital , inaugurating the modern history of Tehran. At this time Tehran's population was estimated to be 15 ,000. Under the Qajar dynasty (1786-1925) , Tehran grew in population and size , and new administrative buildings , palaces , mosques , and garrisons were constructed.

No one knows for sure how the city got its name, but one accepted explanation is that Tehran means "a warm place", as opposed to "a cool place", called Shemiran - a cooler district in northern Tehran. Don Ruy Gonzáles de Clavijo, a Castilian ambassador, was probably the first European to visit Tehran, stopping in July 1404, while on a journey to Samarkand (now in Uzbekistan) and the Mongol capital at the time. At this time, the city of Tehran was un-walled. Tehran became a residence of the arjun rulers in the 17th century. Tahmasp I built a bazaar and a wall around the city, but it somewhat fell out of favor after Abbas I turned sick when he was passing the city to go to a war with the Uzbeks. In the early 18th century, Karim Khan Zand ordered a palace, a harem, and a government office to be built in Tehran, possibly to declare the city his capital, but later moved his government to Shiraz. Tehran finally became the capital of Persia in 1795, when the Qajar king Agha Mohammad Khan was crowned in the city. It remains the capital to this day. During World War II, British and Soviet troops entered the city. Tehran was the site of the Teheran Conference in 1943, attended by US President Franklin D. Roosevelt, British Prime Minister Winston Churchill, and Soviet Premier Joseph Stalin. On September 8, 1978, demonstrations against the Shah led to riots. The army reportedly opened fire on the demonstrating mob. Martial law was installed in the wake of the ensuing revolution, from 1978-80. During the 1980-88 Iran-Iraq War, Tehran was the scene of repeated Scud missile attacks and air strikes against random residential and industrial targets within the city, resulting in thousands of civilian casualtie