Abstract
The architecture of mosques has undergone various changes in different periods and each historical period has shown its own characteristics. The Khwarazmshahi period is a historical period in which architectural history researchers, due to the shortness of this period and the Mongol invasion, sometimes include the buildings left over from this period as Seljuk or Ilkhanid works. By examining the examples of the two periods, it can be seen that although the architecture of the Khwarazmshahi period was formed in continuation of the Seljuk architecture, it did not follow it completely. The purpose of the research is to investigate features of Zavareh and Gonabad mosques as prominent buildings of the Seljuks and the Khwarazmshahi to pay at the architectural similarities of the two mosques in two successive periods and the architectural differences of the two mosques in two different climates. Zavareh mosque is located in Isfahan, the capital of Seljuk period, and Gonabad mosque is located in Khorasan region, like other mosques of Khwarazmshahi period. By studying the library sources, the theoretical foundations were obtained and the spatial and functional structure of the two mosques were analyzed using the analytical-descriptive strategy along with the comparative comparison method. The differences between the two mosques were analyzed by reference to library sources. According to the findings of the research, the architecture of the two mosques has common features such as the importance of the south front and its porches, the transmitter role of the yard from binding to receiving and the use of brick, which was followed in the Seljuk and Khwarazmshahi periods. But these two mosques have differences in the number of porches, the placement of the entrance and the nave, and the presence or absence of the dome and minaret. In fact, the architecture of Gonabad Mosque has similarities with Zavareh Mosque in terms of space and function, but it has its own characteristics in the organization of the space and it has used the two-porch style without a dome, which is common in most mosques in Khorasan, While the Zavareh mosque has a unique grandeur with the use of a dome and vertical elements. 
Keywords: Zavareh Mosque, Gonabad Mosque, Spatial and Functional Structure, Comparative Comparison.

Introduction
The architecture of mosques has a special place in Islamic art and is a clear manifestation of art in a holy and blessed space and has long been the bed of historical, social, political, social and cultural events (Bemanian et al., 2010: 38). Examining the architectural art of different eras begins with the architecture of mosques, because the mosque, which was the first base and center of gathering of Muslims, in all eras and Islamic lands, its building is very important (Hatam, 2000).
The Seljuk period and the Khwarazmshahi period are considered as two consecutive historical periods in the current research, and the two mosques of Zavareh and Gonabad are representative examples of these two periods, which express their architectural characteristics. The mosques of each historical period are influenced by the features of their previous period, and it is expected that Gonabad Jame Mosque (Khwarazmshahi period) has been influenced by the architectural features of Zavareh Jame Mosque (Seljuk period). The reason for choosing these two examples is that these two mosques as a complete example express the characteristics of their periods and have more complete information than other works of these periods. For this reason, one of the samples was selected in Isfahan and the other in Khorasan, where the Khwarazmshahs ruled the Khwarazm region and the eastern provinces, and most of the known works of this period have the Khwarazmshahi (Khorasani) style. Therefore, it is expected that the difference in the region and climate, along with other factors, will cause differences in the spatial and functional structure of the two mosques. Based on this, the first question of the research is that Gonabad Jame Mosque as an indicator example of Khwarazmshahi period has been influenced to what extent by the spatial and functional features of Zavareh Mosque as an indicator example of its previous period? The second question of the research is, what factors have influenced the difference in the spatial and functional structure of the two mosques in addition to the regional characteristics?
In this research, with the aim of examining the architectural similarities and differences of the two mosques, it has been first pointed out to know the architectural structure of the mosques of the Seljuk and Khwarazmshahi periods; Then, by looking at the spatial and functional features of the two mosques of Zavareh and Gonabad in three scales, macro, medium and micro, their comparative comparison and analysis of existing differences has been done.

Discussion
Order to explain the similarities and differences between the two mosques and to analyze the existing differences, the spatial and functional structure of the two mosques in Zavareh and Gonabad were investigated in three scales: macro, medium and micro. In the macro scale (city), the location of the mosque is defined by factors such as physical connection and continuity, spatial features and functional scale (local or city)، (Soltani Fard & Seyed Moradi, 2016: 108-109). Therefore, the relationship between comprehensive mosques and urban structure was analyzed as a macro scale in this research. As a physical element, the mosque is made up of defined elements such as the entrance, mezzanine, porch, Shabestan, dome, minaret, altar, etc. (Zahabi, 2018: 3-4). In this research, these elements are referred to as medium scale. These elements are mutually related and form the functional-spatial feature of the mosque complex (Soltanifard and Seyed Moradi, 2015: 108-109). According to the constituent elements of the mosques, variables are defined for the analysis of the two mosques at the medium level, which are based on the analysis of the physical pattern, spatial diagram, spatial diversity and spatial-movement hierarchy, as well as the examination of each of the constituent elements and spaces of the mosques (entrance, courtyard and pool), porches, Shabestan and dome). Considering the importance of decorations in Islamic architecture, variables such as decorations and materials used in the building were used as a micro scale.
After the initial description the mosques, based on its spatial and functional structure, a comparative comparison of the data obtained in three Scale has been carried out. The findings of the research show that the architecture of the two mosques of Zavareh and Gonabad have similarities with each other, which is due to the consecutive period of their construction; including the connection with the city, the number of entrances, the equal ratio of open and semi-open spaces, having a central courtyard and organizing the surrounding spaces for transfer and arrival to the final destination, the importance of the south front and its porches, observing the spatial and movement hierarchies, the number of Shabestan, the use of bricks, natural and geometric motifs. But, the regional diversity and the Physical pattern affected by it have caused differences in the two mosques; including the difference in the number of porches, the difference in the shape and size of the courtyard, the difference in the dominance of the central geometry, the difference in the height of the porches, the difference in the opening and depth of the south porch, the difference in the allocation of the space of the Shabestan and its placement, the difference in the hierarchy of movement towards Shabestan, the difference in the presence and absence of the dome and minaret, and the difference in the location of the altar. In addition to regional diversity, other factors affect the differences between the two mosques; among these differences, we can mention the difference in location in the city, the placement of the entrance spaces, the strength of the building and the type of decorations.
 
Conclusion
The results of the comparative comparison of the two mosques of Zavareh and Gonabad in three scales, micro, medium and macro, show that the major difference between the two mosques occurs in the middle scale of the spatial-functional structure of the mosques. In fact, all the differences mentioned in the medium scale, except for the placement of inputs, are caused by climatic, regional factors and the physical pattern affected by it. The differences mentioned in the macro and micro scale, as well as the difference in the placement of inputs in the medium scale caused by other factors, are mentioned. 
In general, Gonabad Mosque has similarities with Zavareh Mosque in its spatial and functional structure, but the organization of its spaces has unique features; So that it has used the style of two porches and without a dome, which was common in many mosques in the Khorasan region. In return, Zavareh Mosque, like many mosques of the Seljuk period, by using the dome and vertical elements and in the four-porch style, unparalleled grandeur has been found.