The population of Iran is the result of that progressive expansion towards the S of the Central Asian and Indo-European populations, which on the one hand conquered the Indus valley (the Ari peoples), on the other, crossing the Kopetdag, the Iranian plateau. The Kopetdag still remained, like more in E Paropamiso, the dividing element between the Iranian area and the Turkish area. However, there are several groups of Turks in Iran: Azerbaijanis who represent a quarter of the population, Turkmen who live E of the Caspian Sea, Kashkai, nomads and semi-nomads from Zagros, descendants of a horde that arrived in the country following the invasion. Mongolian. However, the majority of the populations is given by Iranians, among which, however, ethnic groups are recognized that have preserved their unity of feudal promotion: among these groups the main ones are those represented by the great nomadic tribes of Zagros, including the luri, the bactiari and the Kurds themselves (the latter represent, in Iranian territory, only a fraction of the larger group that occupies north-eastern Iraq and eastern Turkey); another important group is that of the Baluchi in the Southeast of the country. The real Iranians represent 51% of the total and not only have a common paternity but have also been profoundly shaped over time by a culture that has never lost its deep unitary ties. These refer primarily to the Achaemenid empire, which for the first time linked the Iranian territory under a single organization, creating nodal centers that were no longer abandoned and placing the basic nucleus of the country in the Fārs. Islamization was also important, which exalted urbanism, consolidating that territorial structure which has its centers in the great oases already privileged previously. Under the dominion of the Safavids, urbanism was again reactivated by the economic and commercial liveliness of the country, which found its refined capital in Eṣfahān. With the dynasty of the Cagiari the capital was transferred to Teheran, and thus there was a territorial reorganization which, already under the dominion of Nādir Shāh, had been marked by a new land regime (which favored the reconversion of feudalism in that long-lasting land to the second half of the 20th century) and by an extensive sedentarization of the nomadic populations. During the twentieth century, after a long period of decline and isolation, the country opened up to Western influence thanks to the policy of Reẓā Pahlavī with which all those characteristic phenomena connected to modernization began, including population growth, development of urbanism, enhancement of the more functional areas compared to traffic to the disadvantage of the poorer and more peripheral ones. The population of Iran has undergone slight variations, which however do not substantially change the general picture of the Iranian demographic situation which is characterized by a contained growth rate. The average density is 44 inhabitants / km², with much higher percentages in the capital area, in the northern provinces and in those located on the Caspian Sea. On the relative demographic stability of Iran they exerted, in the last decade of the century. In the twentieth and early years of the following century, a certain influence was given to the flows of refugees from Afghanistan and Iraq, some of whom were repatriated (850,000 Afghans who returned home between 2002 and 2007). The population of the countryside still represents almost 35% of the total. There are groups of nomads, especially in Zagros, who make seasonal migrations between the coastal plains facing the Persian Gulf (warm lands or Garmsir) and the highland pastures (fresh lands or Sardsir). Seminomads are found in Baluchistan, Elburz and Azerbaijan. But most of the population, after the sedentarization processes, lives in villages. They are of different sizes and are collected in oases, more or less extensive according to the abundance of water, drawn from the qanat, the underground channels tens of kilometers long that allow the settlements to be located even far from the foothills, in the open plains, where the soils are better. To this distribution in the plains we owe the qal’a type villages, that is those fortified centers, numerous especially in Khorāsān, whose origin is very ancient and whose diffusion seems to be linked to the insecurity left by the Mongol invasion of Genghis Khān. These villages, however, stood as a defense against the incursions of the nomads who, in past centuries, frequently took place on the northern front open to Turkmenistan (the Alexander dam, the Sād-e-Iskender, is a defense element that had some functions similar to those of the Chinese wall). In the oases, in the areas of more intensive agriculture, the compact village has been replaced in some cases by the scattered house (built of mud and ventilated by means of air vents; well diffrent is the stately townhouse that derives from ancient traditions and is of considerable refinement). However, the ancient phenomenon of the concentration of the population in the few arable and water-rich areas has been accompanied by that of the tendency towards urbanization. The poverty of agriculture and the presence of commercial, cultural and religious activities in urban centers have always represented an incentive for development, but the start of an industrialization process in the cities has attracted a substantial influx of population. The most striking example of this accelerated urbanism is Tehran, an immense agglomeration of miserable neighborhoods, which are violently opposed to the modern and luxurious ones of the upper part, on the hospitable slopes of Kolum Bartek. The city has grown dramatically in the last decades of the twentieth century: in 1930 it had only 120,000 inhabitants, while at the 2006 census it had almost 8 million inhabitants, also considering the vast suburban shanty towns. This is due to the fact that it concentrates the main activities, with respect to which it is favored by its nodal position towards the most prosperous and populous areas of the country. The capital is directly connected with the other cities of the country, central hubs, in turn, of distinct regions: Tabrīz, the keystone of the North-West, Eṣfahān of the Center-South and Mashhad of the North-East. In particular, Eṣfahān has had a notable development: the ancient Safavid capital represents the typical Persian city, with its orderly urban planning developed around the Maydān-i-Sahāh, with its magnificent monuments and with the nearby bazaar divided into craft and commercial districts ; it has retained much of its charm and at the same time has been industrializing and multiplying its activities. On the route between Eṣfahān and the capital is Qom, the holy Shiite city capital of the province of the same name. Eṣfahān is also located on the important road that, towards the S, continues up to Shīrāz, the capital of Fārs, a city also in a notable phase of development and rich in commercial and industrial activities. Tabrīz performs similar functions, whose importance is increased by its position on the arteries connecting the capital to Turkey, Armenia and Azerbaijan. On Mashhad, at the opposite end of the country, the whole Khorāsān gravitates; moreover, joined to the capital by a railway line, it is located on the route that leads to the Afghan border and is at the center of a rich and vast oasis. It is also a prestigious religious center, frequented by thousands of pilgrims. The cities of the Caspian directly belong to Tehran, of which Rasht is the largest. Although they are now united by good communications with the capital, the cities that are located on the edge of the deserts have had less development, centers of ancient origin such as Yazd and Kermān, located on the route that continues up to Zāhedān, a city of recent development near the border with Pakistan. Ahvāz, the capital of Khuzistān and an important cultural and economic location, is also an important city, which is around one million inhabitants, while ,bādān, a port of embarkation for oil and a large petrochemical center, is near the Persian Gulf. Karaj (near Tehran) Bandar-e Khomenī and Bandar-e ‘Abbās (port cities) have assumed a more important role.