The Evolution of the Ivan in the External Formation of Traditional Iranian Architecture and Its Influence on Neighboring Countries

Introduction:
The porch or Iwan is one of the important elements of traditional Iranian structures, which has been classified into two types: columned and column less from the Parthian period to the present day. The Iwan appeared an important role in the formation of residential spaces in a residential unit, into two areas: private and public. Also, in the lighting and spatial arrangement of traditional houses, respect for nature and the use of eco- friendly and inexpensive materials, establishing social relations and communication between the outside and inside of the building are among the roles of the Iwan in the architecture of a residential space and it contains some components of green architecture.
Research Objective:
The aim of this research is to study the evolution and understanding of the Iwan or porch and its comparable elements and to obtain evidence on the origin of the porch and its role in separating the functional spaces of the house into two areas: external and internal.
Methodology:
The present research is fundamentally theoretical in terms of its purpose. The research method is descriptive- analytical. The research strategy is historical, interpretive and comparative.
Findings and Discussions:
The courtyard and the porch or Iwan, as two influential elements in the spatial arrangement of traditional Iranian structures, provide the possibility of light, access, and visual order of a structure. The research data in examining the evolution and formation of these architectural elements include historical monuments identified in Iran and Mesopotamia. These elements, in their historical process and evolution, have led to the emergence of two areas: the interior (private part and the shrine) and the exterior (reception part) in the residential structure. In research the evolution of the architecture of courtyard houses with porches, one encounters plans of structures such as the Beit- Hilani (in the Hittite and Assyrian civilizations), the Apadana of Iranian origin (Median and Achaemenid), the Tarma in Iraq and Iran, the Parthian and Sassanid porches, and the Hellenistic peristyle, which indicate the commonalities and differences between these types of structures.
Conclusion:
 The first time Iwan developments leading to the formation of the porch structure took place in the Dahaneh-e-Gholaman site in Sistan. In this place, several relatively square buildings belonging to the Achaemenid period were built with the plan of room-portico-room and a courtyard in the center. This plan was changed and in the Aï Khanoum Site (first half of the 2nd century BC) it is seen in the form of a square building with a central courtyard with pillared porches on all four sides of the courtyard (room-porch-room). Then in the Kuh-e Khwaja building (first century AD), the porch columns were removed and this plan became common throughout the Parthian territory, even in Mesopotamia. After Islam, the construction of courtyard houses with Iwan continued in Islamic lands. The emergence of the Seljuks, Mamluks, and then the Ottomans, who were familiar with Iranian culture, was very effective in expanding this design, and even the names of many architectural spaces in Iraq and Syria are of Iranian origin (for example: Sardab, Hall, Ab- Anbar).
Residential houses in Iraq and Iran have many similarities in form, function, and even names (Hall, Orsi, Sardab, etc.). Orsi is the name of a space in Tabriz houses, also called Haft-Dari, which is reserved for special guests and is considered a winter residence (the northern part of the courtyard). In Iraq, there is also a space called Orsi, which is considered the most important room in the house, and is located behind the Tarma.
Despite the similarities with the houses in Iraq and Syria, the Iranian house also has some differences that are the result of the influence of the indigenous architectural culture of Mesopotamia and the Eastern Mediterranean. In the Syrian region, reception units (Qa’a) are mainly in the form of an inverted T-plan or have “three Iwans”. The T-plan is seen in Iraq in the form of a Tarma-Iwan or Tarma-Orsi combination. The spatial combination with the T-plan existed from the third millennium BC in Ur to the mosques of the third century 9 A.D (for example: Abu Dolaf Mosque) in Mesopotamia and Syria and was a local and stable design of the region. On the other hand, the spatial arrangement of the Qa’a in Syria was an adaptation of the ancient Trinity (three-part) plan in the architecture of the Eastern Mediterranean (or the eastern territory of ancient Rome).
Limitations of the research include the few and decentralized studies in the field of comparative plans and comparisons of the iwan and other architectural elements related to it in neighboring countries (especially Iraq, Syria and present-day Turkey). Therefore, there is no comprehensive knowledge of the spaces related to the Iwan in this region. Since the porch contains some of the key components of green architecture, such as respect for nature, the use of endemic and inexpensive materials, establishing social relationships, communication outside and inside the building, and even the appropriate use of light and its transfer to other spaces of the building, it is suggested that by recognizing such traditional architectural elements in the cultural realm of Iran and combining them with contemporary architecture, a new horizon can be opened in the preparation of conceptual and practical models in green architecture.