Abstract
Throughout history, historical architectural works have been maintained, changed in use, expanded spatially, and had architectural elements added. These interventions and additions contribute to the dynamic nature of a structure. However, dealing with these additions, whether through familiarization, complementary conservation, or occupation of the constituent elements, can be a complex process. Proper actions in conservation, stabilization or destruction require an understanding of the reasons behind the existence of each layer, which could provide the basis for essential actions. This research aims to examine the formation of historical layers over time. It seeks to address questions such as the role of historical layers in conservation decisions and the process of a building’s evolution. This study is classified as applied and developmental research, utilizing a combination of strategies and research methods. It will be a qualitative research study based on a case study approach, utilizing archival documents, fieldwork, and library resources, and documentary data collection. The study will place a particular emphasis on conducting field observations. The Pir Bakran building has been chosen as an important architectural feature to illustrate the path towards understanding buildings with multiple historical layers. It heavily relies on the research method based on case samples and data analysis. Ultimately, this research emphasizes the importance of a comprehensive understanding of historical structures and their different aspects throughout the conservation process. This includes accurate knowledge of the work’s existence, nature, and the recognition of all historical layers and the reasons behind their creation as the work has developed and evolved over time. Such understanding forms the foundation for effective and proper conservation.
Keywords: Architectural Extensions, Historical Layers, Evidence- Based Restoration, Pir Bakran Mansion.

Introduction
The 11th article of the Venice charter suggests that the valid contributions of all periods to the building of a monument must be respected, since unity of style is not the aim of a restoration. When a building includes the superimposed work of different periods, the revealing of the underlying state can only be justified in exceptional circumstances and when what is removed is of little interest and the material which is brought to light is of great historical, archaeological or aesthetic value, and its state of preservation good enough to justify the action. Evaluation of the importance of the elements involved and the decision as to what may be destroyed cannot rest solely on the individual in charge of the work. So, it would appear that the exceptions allow for intervention in the structure and the removal of layers, especially extensions. But there is a question: what feature of that particular layer enables intervention?
However, many theorists argue that the presence of historical layers within a structure affects its authenticity, particularly in light of the fact that material integrity is taken into account when determining the historical accuracy of a work The Nara document (1994) of course, this issue is related to various perceptions and the gradual emergence of the notion of authenticity. The Nara document (ICOMOS, 1994) brought up a never-before-discussed issue: the varying perspectives on authenticity across different cultures. Effective conservation calls for the accurate reading of historical layers in valuable buildings and an understanding of the factors that led to the formation of additional layers in various eras. The research’s central premise is that historical layers are intentionally created over time.  
The hypothesis of this research is “creation of historical layers over time is purposeful”. The research questions include: What role do historical layers play in historical decision-making? How does the process of building evolution occur? What are the reasons for the formation of historical layers in a building? Will be. The historical monument of Pir Bakran was the subject of a case study that was looked into in order to comprehensively and deeply clarify the topic, content and understanding of the phenomenon within the context. Due to this monument’s historical feature, varied uses throughout its history, and multiple significant historical layers with various causes for formation, it has received discussion that hasn’t been done before. It will be a qualitative research based on a case study approach, utilizing archive documents, fieldwork, and library and documentary data collection, with a particular emphasis on field observations. The so-called process that should be followed in order to understand the building with different historical layers is indicated by an examination of the case study’s outputs.

Identified Traces
Over time, conservation theories from the 20th century have revealed the various facets of authenticity. These studies have demonstrated that throughout its history, authenticity has been a variable and relative concept. Theoretically, the approach to the idea of authenticity in charters and documents has significant implications for conservation and interventions, particularly when choices are made regarding the conservation or removal of historical layers. It has been looked over and read again to come to a conclusion about the historical layers. The emphasis was laid on the necessity to respect and maintain the authenticity of historic monuments as well as to safeguard them an appropriate use “no less as works of art then as historical evidence”. These aspects, in fact. From the essence of the theories of conservation, the questions around which debates had been going on for more than a century, and where opinions had often been divided (Jokilehto, 2005: 422).
Because the building’s historical eras reveal the history of the monument and provide tangible and intangible proof of the decisions made during its lifespan, entire portions of the evidence should be preserved. Conservation of historical evidence is crucial because loss shouldn’t happen as a result of preservation since a monument’s history can be viewed as a component of its value. The responsibility for safeguarding the historical layer, which implies the building’s life, survival, and durability, rests with the decision-makers. Buildings’ historical layers all work together to create a cohesive whole and give it consistency. In fact, every layer is a historical record of its time and shouldn’t be altered, moved, or removed during the intervention. The originality of a building’s overall design is also reflected in the originality of the building’s component parts or historical layers.

Conclusion 
Based on the research, which included details and changes identified in the Pir Bakran tomb’s architectural elements of and specific categories, determining the exact date of extension and added decorations with using inscriptions, old photographs, archaeological findings and architectural evidence, it determines that the Pir Bakran tomb has different and numerous historical periods, which makes it particularly complicated. This building’s construction began with a small adobe room, which was later joined by a lofty three-story structure, and due to political, religious and geological developments, decorative and structural elements with different periods are added to it. Some of the extensions were created while completing the Pir Bakran tomb and related to the construction period of the building. The expansion and additional elements of these periods, such as the additional belt, the southeast entrance, etc. shows the structural and decorative evolution of the building. In fact, a historical monument is the result of the combination of various historical layers that have formed over time and blended together. These layers have experienced ups and downs and, at times, have become intertwined, ultimately reaching us in their present state. Therefore, the removal and cleaning of these extensions would be against preservation principles. It has actually been necessary to conserve some of the Pir Bakran building’s historical layers, so it would seem necessary to maintain the structure’s integrity.

Abstract
Historical-archaeological sites are the most important sources to answer the missing links of a nation’s history and civilization. These areas always have diverse values, which identification and understanding of these values provides the basis for recognizing their protectable aspects. Today, most of these sites in Iran are in vulnerable conditions and their values are being forgotten. The historical-archaeological site of Arjan is located in the Khuzestan plain, which existed from the Elamite era to the Mongol era. Today, this area is in unfavorable conservation conditions. Considering the values and historical importance of the old city of Arjan in the historical periods of Iran, it is very important to protect this area and create a suitable platform to benefit from its values. Among the questions that are answered in this research;1. What are the values of Arjan historical site? 2. What are the challenges of protecting Arjan’s site? 3. How can we achieve conservation principles for the protection and valuation of the historical archaeological site of Arjan in accordance with its values? Accordingly, the objectives of the research؛ 1. Understanding the Arjan site and its conservation challenges; 2. Achieving conservation principles through the analysis of international charters, declarations, conventions and documents and generalizing them to a study sample in order to explain the principles of conservation and value it. The general research method of this research is descriptive-analytical, based on the data collected through library resources and field observations. Then, after analyzing and reviewing international documents and recognizing the historical site of Arjan and its conservation challenges in four fields of cognitive, managerial, legal, physical, and introduction and valuation of the site, principles such as providing information to the public, developing a comprehensive interaction plan, developing public management plans, reversibility of actions, preserving originality and respect for historical and aesthetic values and the physical integrity of the sites are presented.
Keywords: Arjan, Historical-Archaeological Site, Conservation, Historical Values, Introduction of Values.

Introduction
Historical-archaeological sites are the most important sources to answer the missing links of a nation’s history and civilization. These sites will answer many general and partial questions that can be varied and variable over time, so the conservation of the sites is essential for transfer to future generations. Historical archaeological sites have a variety of values and in order to benefit from these values, they are always protected. After archaeological excavations in Iran, these sites are often in vulnerable conditions and are exposed to forgetting their values.
The archaeological site of Arjan is located in the plain of Khuzestan. Arjan is a city with various urban organs in the historical periods of Iran. This site has values, features and elements that are unique in its kind. In 1362, a tomb belonging to Kidin Hotran, one of the Elamite kings, was discovered. Afterwards, Esmaeil Yaghmaei carried out archaeological excavations and studies in the Arjan area and in the area of Maroon Dam and Arjan Grand Mosque and Dr. Abbas Moghaddam conducted archaeological excavations in the area of the oil well during two seasons. With the cessation of excavations in this site, the old city of Arjan, like most historical sites in Iran, was placed in undesirable conditions of conservation.
Research Necessity: The city of Arjan has been standing from the Elamite era to the Mongol era. (Today, this area, despite its historical and archaeological importance and values, is in unfavorable conservation conditions) Considering these values and the historical importance of the ancient city of Arjan in the historical periods of Iran, as well as the necessity of continuing archaeological studies and the availability of its original data among researchers and enthusiasts, it is very important to protect this site and create a suitable platform for benefiting from its values.
Research objectives: 1. Understanding the Arjan site and its conservation challenges; 2. Achieving conservation principles through the analysis of charters, statements, conventions and international documents and generalizing them to a study sample in order to explain the principles of conservation and valuation of the archaeological site of Arjan.
Research Questions: 1. What are the values of Arjan historical site? 2. What are the challenges of protecting Arjan’s site? 3. How can we achieve conservation principles for the protection and valuation of the historical archaeological site of Arjan in accordance with its values?
Research Methodology: The general research method is descriptive-analytical approach. In this research, library studies and field studies have been utilized to gather information.

Discussion
“Archaeological heritage” is a material heritage that includes all traces of human life and includes places that show human activities, abandoned structures, and remnants, along with all the movable cultural objects discovered related to it (ICOMOS, 1990). These sites have a variety of values and in order to benefit from these values, they are always conserved. By reviewing the international documents related to the sites in Table 3, the set of conservation principles in four areas, cognitive, legal and managerial, physical, and the introduction and valuation of the site, has been displayed.
The archaeological site of Arjan with an area of 500 hectares is located on the slopes of Khoiz Mountain and in a wide plain next to the Maroon River, which includes the Mosque Jammeh, the Arjan Dam Bath and Bridge, the Qadamgah of Imam Reza (AS), the Rosh Mehr Building, the Arjan Qanats and the ancient hills. By examining the site and the buildings in it, the values are divided into two categories, cultural values and contemporary economic and social values (Diagram 5). At present, the buildings in the Arjan site are in an undesirable state of conservation and their values are in danger of being forgotten. Through field surveys, the damages and challenges of the Arjan site were identified in four areas, cognitive, legal and managerial, physical and tourism, and were divided into two groups, internal and external factors. Internal factors include cognitive domain, exhaustion (functional physical) and weakness in the infrastructure of the Arjan site, and external factors include lack of alignment of organizations and weakness in the managerial and legal structure. According to the mentioned damages and challenges, by identifying their roots and categorizing them in the form of internal and external factors, we have achieved five conservation challenges related to the historical archaeological site of Arjan (Diagram 4). By adapting the principles of conservation of historical sites to conservation challenges, the principles of conservation of the Arjan site are stated in Table 4.

Conclusion
Historical archaeological sites can be considered as the most important sources for answering the missing links of a nation’s history and civilization. These sites always have a variety of values, and identifying and understanding these values can provide the ground for recognizing their protectable aspects. In the twentieth century (in 1914 and 1916), the main law for the protection of historical sites was adopted, and at that time, terms for the protection of historical sites were created in international charters. In the first part of this research, international charters, documents and conventions were examined in terms of keywords related to historical archaeological sites and the conservation principles related to the sites were identified in 4 areas. In the second part, in relation to the study area, with the knowledge of the old city of Arjan and with an analytical view of field studies, through the analysis, investigation and categorization of the challenges of conserving the historical archaeological site of Arjan and the comparison of the challenges with the principles extracted from international charters, documents and conventions, led to the explanation of the principles of the conservation of the historical archaeological site of Arjan.
The principles of conservation of the Arjan site were presented in four areas: cognitive, managerial, legal, physical, and introduction and valuation of the site. One of the most important principles in the field of cognition was to provide information to the people and to develop a comprehensive interaction plan. Formulation of public management programs, coordination and cooperation between institutions and people, and formulation of intervention laws are among the most important principles in the field of management and law. In the physical field, the reversibility of actions, preservation of originality, continuity of vernacular architecture and native materials, and documentation of changes were mentioned. Respecting the historical and aesthetic values and the physical integrity of historical buildings and sites is one of the most important principles in the field of introducing and valuing the site. It should be noted that these cases, along with other conservation principles proposed in the research, lead to the improvement of the condition of the archaeological site of Arjan.