Structure is a complex concept with different meanings. In this paper, I've tried, by tracing the origins of the word and history of its changes, to show its meanings and uses in urban studies. On this basis, I'll discuss how by adopting different approaches based upon different concepts of structure one can try to recognize the basic structure of the Iranian pre-modern cities and as a case I’ll employ it to determine the basic structure of Tehran within its wall, built by Shah Tahmasp of Safavid kings, in Qajarid period (until mid nineteenth century).

This study shows that coexistence of different concepts of the structure has resulted in different meanings for it; although it has been used by modern architects and urban planners as if being a thing. Being as a thing is what is assumed in studies on basic structure of the cities. Recognizing main structure with a spatial analysis which is a combination of typological, morphological and symbolic meaning analysis can define the essential part of the spatial form which constitutes its symbolic and durable part and other parts of the city follow its spatial form. Thus, the essential part structures the form of the city. This study shows that an unchangeable form for basic structure of Iranian cities can not reveal the reality of urban spatial structure of Iranian cities in different periods and especially in later -Safavid and Qajarid - periods. So, studies that have determined the urban spatial structure of Iranian cites as a rigid form during its history of Islamic period (for example model proposed by Gaube) can’t be generalized to all Iranian cities in their whole Islamic times. This is especially true for cities that evolved during early modern times, from Safavid period on. Rapid expansion of some cities in this era, for example the case of Tehran in Qajarid Period, made their main structure subject to rapid and sometimes broad changes. Analysis of urban spatial structure of Tehran, from the time it was chosen as capital of Qajar dynasty to demolition of its Safavid walls in mid 19^th century shows this state of changing conditions. By employing typological, morphological and signification analysis; it has been concluded that the basic structure of Tehran in this period, not only included paths and places which were along the main axis leading from gates to city center(as described by Gaube or  other scholars in their studies of basic structure of Iranian cites), but also included paths and places in other parts of the city which were in the course of rapid construction especially along the water canals(qanats).Thus, the findings also shows that main structure of the city was in accordance with the hydrographic and tectonic structure of the city.

By combination of urban spatial structure analysis with search for structures which were meaningful for people, other structures can be defined in pre-modern Iranian cities, especially a secondary spatial structure in Qajarid period which was formed on the basis of people’s cultural, social and everyday life.