In a pioneering work that first drew attention to the individuality of Iranian cities in the Islamic world, Jean Aubin examined the causes for the growth of settlements on the Iranian Plateau from the three aspects of geography, economics and politics.2 His wideranging arguments may be summarized as follows. Geographical factors took precedence in the development of cities on the dry Iranian Plateau, in that they were built on the edges of the plateau where there was a supply of water. These cities were surrounded by an extensive rural zone, from which they cannot be considered separately. Even when natural conditions were disadvantageous, though, economic factors might prevail, as where cities grew up on trade routes. Such cities however would decline when trade routes changed, as is well illustrated in Southern Iran. Cities also
developed through political factors, such as by occupying an important strategic position, or by being connected with a particular interest group. Those cities which grew up in the period political power was exerted by nomads fall into the same categories. Their routes were different to the regular trade routes and passed through many areas of adverse geographical conditions, yet particularly in the Mongol period a large number of structures were built along them. These however had only a temporary existence, owing to princely whim, and they disappeared once the rulers grew to favour the traditional cities. Only Sultaniyya survived to the seventeenth century. This city followed a pattern well known in Central Asia from early times, that of a union of a town with a surrounding pastoral area (association de villepâturage), and its survival owes to three factors: that it was a commercial centre for nomadic people, that it was strategically important, and that it was situated on the east-west trade route.