Abstract
Using stucco as decoration in buildings has a long precedent. Scrutinizing the surviving edifice from historical periods shows that the art of plastering has been methodical and has a special style since the Parthian era. These methods evolved in the Sassanid era and continued with nuance in the Islamic era. Our knowledge of the art of stucco decoration of the Sassanid period is mostly based on the excavation of several important sites of this period, including the historic city of Bishapur. Bishapur is the center of the Shapur-province which was considered to be one of the cities or the state of five states of Persia and it was established during the reign of Shapur I, the second Sassanid emperor. Manifold artworks have been found in Bishapour’s excavation such as unique mosaic paintings as well as plastering and painting on plaster, especially in the part of the royal citadel. Many of these findings which are some important artifacts and features, exploring in the ninth season of excavation such as the revelation of architectural spaces in the south of the mosaic porch in the part called “Royal Citadel” and stone objects such as mortars, Xunak: stone table, stone statues made of marble and decorative beads, glass kilns and pieces of glassware, pottery and metal. The most important architectural works revealed in the excavation are the corridors on the south side of the mosaic porch, rooms with plaster works’ niches, while some of them are painted and decorated with red ocher clay, plaster of the walls, and plaster of the floor of architectural spaces have been found in these rooms as well. The plaster artworks are mostly included the parallel strips that are used at the edges of niches and entrances. Gypsum mosaic porch decorations include plaster coating and painting on the plaster, as well as plaster works and remains. Considering that all these pieces belong to the Sassanid period, the main question in this research is: How were they made? The method of data collection has been done in two ways, fieldwork and by researching in the library in this article. Besides, the tendency in this research was to introduce and analyze these findings in the context of the plaster art of the Sassanid period in this historical city
Keywords: Sassanid Period, Bishapur, Architectur Decorations, Stucco.

Introduction
The city of Bishapur, with an area of about 155 hectares, is an enormous area where comprehensive exploration is impossible in a short time. The ninth season excavation program started on 22/05/2011 and lasted until 6/07/2011.
The most important objects found from the excavation were: Three pieces of human sculpture of a man as well as a piece of human sculpture of a woman, both made of marble. A significant number of archaeological findings in the ninth season of the excavation of the historic city of Bishapur were metal fragments. The metal findings based on the type of metals are iron, copper, and silver, in order of frequency respectively. In addition to these findings, several earthenware jars and pots of different dimensions are among the main objects of the ninth season of the excavation of the historical city of Bishapur. For the first time, in the same excavation season, all the pottery pieces founded in the excavation, have been collected, washed, and classified. The first category includes decorative objects such as statues and precious and semi-precious stones, which include ring agate stones and necklace beads, as well as turquoise stones; and the second category, including oil trays, mortars, and stone tables which is known as “Xunak” by the locals. There were also recovered many pieces of broken glassware along with a glass kiln during the ninth season of excavating the historic city of Bishapur. In the same season, manifold remnants of glass-making furnaces and mosaic pieces were discovered. The most important findings of architectural works include the corridors on the south side of the mosaic porch, rooms with bedside niches, which are sometimes painted and decorated with red ocher mud. Another finding in this season was plaster pieces which is the purpose of writing this article, is to introduce and classify these plaster findings.

Identified Traces
The ninth season of the excavation in the historical city of Bishapur focused on the south and west sides of the mosaic porch, and although in the development of the excavation and the pursuit of walls and spaces, the scope of the excavation was extended to the eastern boreholes; But most of the findings come from southern boreholes, especially the D-3, D-4, and D-5. In terms of plastering and decorations, these three boreholes were richer than the other boreholes.
In general, there are two types of indicator hypotheses about the construction of gypsum decorations; In the first hypothesis, it is believed that the plaster decorations in this area were drawn on the walls at once, and then the artist created his desired designs on the plaster with a tool similar to a scraper; But in the second hypothesis, it is believed that the plaster’s decorations were made in the form of molding and then installed in place. Given the available evidence, it is not wise to simply accept or reject any of these theories. Applying and combining these two methods was certainly not impossible, and the artists of the Sassanid period could create innovative and new methods in this field; Because it seems that in some cases the designs have been prepared by molding method and in some cases, the plasters have been applied on the wall at once; Thus, in Bishapur, the two methods of in-situ shaping and fabrication using mold can be considered as the main methods in performing plastering techniques. In the in-situ shaping method, after applying the gypsum paste on the desired surface, such as a wall or ceiling, etc., and the expiration of the gypsum setting to a suitable level that does not cause the gypsum to fall, the gypsum master forms the gypsum mortar. In the method of using the mold, it is done in two ways: in situ and prefabricated. In the in-situ method, gypsum mortar is poured into a one-piece or multi-piece wooden mold that has been pre-made, and in some cases, it is injected and after setting the plaster and kneading it, it separates the mold from it and the masterworks on its joinery. In the prefabricated mold method, all the parts are pre-made and the master connects them and after joining all the parts, he pays them. Gypsum pieces with geometric designs found from the ninth season of excavation in Bishapur are usually mold-making and do not have various shapes, and are usually spoon-shaped, in other words, tube-shaped. It seems that all these parts have been used to cover around the ledges, corners of walls, windows, and doors. Parts of this type of plastering around a ledge have also been found. Another example of stucco is “shell designs”. These pieces represent a bunch of bivalve mussels. The use of these parts is all as fillets next to the dome and porch as well as the corners of the rooms. These pieces were also made by molding and probably did this on the spot.
Other parts are plaques that are found in the form of broken pieces. These parts usually belong to the edge of the plate and are only one part of the center of the plate. The plaques sometimes have human motifs depicting kings, princes, princes, and gods, and provide valuable information for researchers in the analysis of political history, art, and archeology. The face of a king or prince was found inside a plaque in the Bishapur, the preliminary stages of which have been completed and the results will be published in the future. The designs of these gypsum boards are usually geometric and floral. The geometric patterns are mostly related to the square border of the plate. Several pieces of red and black colored plaster are also obtained, which are related to flat walls.
The artists of the Sassanid period could create innovative and new methods in the field of plastering; Because it seems that in some cases the designs have been prepared by molding method and in some cases, the plastering has been applied on the wall all at once; Thus, in Bishapour, the two methods of in-situ shaping and fabrication using molds can be considered as the main methods in performing plastering techniques, which are usually prefabricated parts made in two sizes; One of them is 12 x 12 cm and the other is 18 x 18 cm.

Conclusion
From all the discovered artifacts, little information can be figured out from the plastering around the ledges. Upper back injuries are more common than lower back injuries. These plasters consist of two categories; The first category is plastering that is prefabricated in parts that have been molded due to mass production and the findings of this category are more. The second category is plastering which is built on-site and this category has a greater role. From the first category, most of the stucco is found with a cross and spoon design, and from the second category, there are a little number of gypsum plates. In terms of shape and role, it can almost be said that role limitations are observed in the discovered samples and the designs are not very diverse. These parts had the least similarity with the parts discovered from other Sassanid sites.

Abstract
Lorestan bridges have been of particular importance in different eras due to being located on ancient roads. Bridges built for various purposes, including political, religious and economic, have acted as valley bridges in addition to linking different areas through crossing ravaged rivers of Lorestan at the time such as Kashkan and establishing road safety. Lack of awareness by the local people, the country and the international community of the value of these properties, the destruction of their properties and their associated environments by indigenous peoples and domestic tourists, the lack of a comprehensive and integrated conservation program and the lack of proper budget allocation for their restoration, Their natural context for conservation and restoration has all made these valuable and indigenous properties in the process of destruction. Accordingly, the purpose of the research is to identify the cultural landscape of historical bridges attributed to the Sassanid period of the Kashkan River and to establish a structuralist framework through the analysis of national and international laws, charters, conventions, and treaties to conserve their cultural landscape. In this research, library and field data were collected and four bridges: Kashan, Kelahor-e-Mamulan, pol-e-dokhtar, and Gavmishan were selected as study samples due to historical and architectural values. In the following, recommendations for the conservation of selected bridges’ cultural landscapes were categorized into two categories, generic and specific to the selected bridges themselves using qualitative research method, data analysis, and coding operations at three levels to reach the final results of the research. 
Keywords: Conservation of Cultural Landscape, Historic Bridges, Sassanid Period, Lorestan, Kashkan River.

Introduction
Lorestan province, with its rich and important rivers such as Seymareh, Kashkan and Cesar, has one of the richest flowing water networks. In addition to communicating with the two capitals (Susa-Ekbatan), this province has always established the connection between the old Babylon, then Ctesiphon, and then Baghdad, to Isfahan, through Khorramabad. (Siroux, 1978: 32-33). From other roads, separated from Lorestan, we can refer to Susa to Bisotun and Susa to Masbazan road (Minorsky, 1937). The need for quick and easy access and constant communication between these areas, despite the rich rivers and deep valleys, has led to the construction of huge bridges that makes a man wonder7 (UNESCO, 2016). These bridges have been built to connect large civilizations and some extent of the realization of human rights, religious, ethnic, economic and cultural ties, as well as development, prosperity, security and comfort in difficult mountainous regions (UNESCO, 2016). The undiscovered identity and value of these works for the indigenous people of Lorestan and at higher levels, the country and the international community, the destruction of the works themselves and the natural environment, associated with, by indigenous people (intentionally interfering with the cultural landscape of the bridges), lack of comprehensive conservation and restoration plans and lack of necessary credit allocations from organizations, entrusted with these works, the non-formal and mere physical restoration of some properties, regardless of the context in which, they are formed, have all made these valuable properties of art and cultural landscape associated with, to increasing degradation. In Lorestan cultural domain, these properties have been constructed with the highest quality of locating and building, and study of these works and conservation challenges of their cultural landscapes, can certainly Conserve bridges, with addition follows:
• To illuminate and conserve various historical layers of the region;
• To preserve the natural environment (including river, valley, etc.) where the bridges are located;
• For legibility and conservation of the region’s indigenous culture and
• To achieve construction technologies of bridges, for future conservation and restoration of these properties.
This research seeks to identify the Cultural landscape of Historic Bridges on the River Kashkan and its conservation challenges, in order to provide a basis for helping, define a systematic model to conserve its cultural landscape. In this regard, the following question is defined as:
• What is the definition of the cultural landscape of historic Bridges on the River Kashkan?
• How can a systematic, structuralist model be achieved to conserve the cultural landscape of historic bridges over the Kashkan River?

Discussion
According to the epigraph left by the bridge, Badr-ibn-Hasanwayeh has introduced himself as a constructor to this bridges. The cultural landscape of these Bridges is an integrated collection, interacting with humans over time in the geographical domain of middle Zagros. Despite the vagueness of the “cultural landscape” meanings, today this word has become one of the most controversial words in the World Heritage Convention. Challenges are coming into place when modern science cannot face the challenges of different levels and disciplines (Zibalkalam, 2018). Conservation is also no exception to this and has undergone various changes over time to respond to problems, encountered in conservation. The analysis of this research is carried out through “codifying” at three levels: first cycle codifying, second cycle (middle) codifying, and third or final cycle codifying (post-coding). The codes were reviewed and stored to verify the qualitative data, in order to identify conservation principles of the cultural landscape of these Bridge (the core of the research), at the final stage (Afshar, 2014). In the following, by integrating, the results of code analysis are compatible with the dispersive components of the image (Giviyan, 2016). In the following, recommendations for the conservation of selected bridges’ cultural landscapes were categorized into two categories, generic and specific to the selected bridges themselves using qualitative research method, data analysis, and coding operations at three levels to reach the final results of the research.

Conclusion
This research, in the form of fundamental-applied research, was able to identify the conservation of the cultural landscapes of the studied historical bridges and make them applicable to other similar historical bridges in Lorestan. This study was able to introduce recommendations in two general categories Generic and specific to the bridges themselves. In response to the first part of the research question, the concepts and constituent elements of the cultural landscape of historical bridges were identified through the library, field studies, and analysis of various concepts in the subject literature and in accordance with the native conditions of the cultural landscape under study. In answer to the second part of the research question, it can be said that by analyzing the collected literature and taking a look at field studies, by examining and analyzing the challenges of conserving cultural landscapes and the meanings and concepts of conservation in national charters, conventions and treaties, and International; Investigating and analyzing the meanings and concepts of cultural landscapes in national and international charters, conventions and treaties. These recommendations, since taken from the very context of the aforementioned research and context, have been categorized into a specific framework and have created a systematic model for the conservation of the cultural landscapes of the historical bridges studied.