Abstract
The interaction of cultures in prehistoric Iran has always been one of the most important and complex topics in Iranian archeology. Such connections in different regions of Iran show the relationships of cultures and their effects on each other. During the fifth and fourth millennia, these connections became more extensive and significant. During this period in the South Zagros region, between Fars, Chaharmahal and Bakhtiari (Bakhtiari region) and Khuzestan regions, close cultural ties were formed, which are more than anything else reflected in the pottery collections of Bakhtiari region. Alain Zagarel in his studies in different parts of Bakhtiari region points out that during this period, this region has received many cultural influences from Fars and Khuzestan regions. In this article, the cultural relations that took place during the chalcolithic Age in the Early / Middle / Late Shushan period of Khuzestan, the Early, Middle and Late Persian periods, as well as in the phases of Alexandria, Chelehgah, Afghan, R1, Lapoei, Shahrak and Borjoui and S17 in Bakhtiari region have been formed, discussed and tried to answer the question of whether there were cultural connections between these areas during the chalcolithic Age or not? According to the studies, it seems that there were cultural connections between these areas during this period. The point that should be mentioned here is that in this study, the cultural influences of Fars and Khuzestan regions on Chaharmahal and Bakhtiari have been considered. The effects of these cultures on different parts of Bakhtiari region are not the same, so that the northern regions of this province during this period were influenced by the cultures of Khuzestan region and southern regions, especially Lordegan city during this period were influenced by the cultures of Fars region.
Keywords: Interaction, chalcolithic, Bakhtiari, Fars, Khuzestan.

Introduction
One of the most important field works done in Bakhtiari region is the activities of Allen Zagarel and Hassan Rezvani during the years 1390-1389. The two main plains of Bakhtiari region, namely Khanmirza, are located 180 km south to southwest of Isfahan, at an altitude of 1800 meters and Shahrekord at an altitude of 2100 meters. Both plains are very fertile pastures, but due to their height, lack of surface water and good soil, they are not suitable for agriculture (Hool, 1390: 132). The sites identified in these areas provide useful information from the pastoral pattern of the pre-pottery period. We are indicating a period of prosperity in the Bakhtiari region. Based on these activities, the question that arises here is whether there was a connection between the Bakhtiari region with Persia and Khuzestan during the Copper and Stone Age? It can be said that the initial study of copper and stone period pottery shows the relationship and close proximity of regional pottery with copper and stone period pottery in Fars (Bakun A and B) And Khuzestan (Middle and New Shushan). However, it seems that the copper and stone pottery of the lords is more similar to the prehistoric pottery of Persia (Bakun A, B and Lepui).

Materials and Methods
Cultural interactions are one of the most important and complex issues in archaeology. In this research, we first tried to study all the sources in this field well, and the pottery related to each region was carefully examined and matched with each other so that we could provide a correct and accurate comparison. Among the important sources that were used in this regard were the reports of excavations, investigations and research activities that took place in these areas during the copper and stone ages. For correct understanding and accurate analysis of the data, it was tried to use the latest archaeological activities and also the latest scientific results published in these areas.

Article Text
The pottery collection of Bakhtiari region provides us with very good information about the Copper and Stone Age, through which the connection between this region and Fars and Khuzestan can be determined. Data from all three phases of the Copper and Stone Age have been found in the Bakhtiari region. Among these, we can refer to the interregional interactions of other regions of Bakhtiari region such as Dashte Farsan with Khuzestan and Fars, and although this has been the case in previous periods(Neolithic), as the evidence shows They show that this trend has significantly increased in the Copper and Stone Age. Currently, studies show that this region is very similar to Fars and Khuzestan. Currently, studies show that this region is very similar to Fars and Khuzestan.A noteworthy point about the settlements of the copper and stone period of Farsan plain is that in this period the southern areas of Farsan plain are very similar to Bacon pottery in Persia, while the pottery of the northern half of this plain is closely similar. They have new Middle Shushan pottery.

Discussion
Based on the conducted research, it can be said that the residents of Bakhtiari region were influenced by the residents of Fars and Khuzestan during the copper and stone ages. Considering that most of the settlements in this area belong to nomads, it can be said that this area was a bridge of communication between these areas during the copper and stone ages. The presence of pottery similar to the cultural materials of the late Neolithic and copper and stone of Fars and Khuzestan indicates the strong connection between the Fars plain and the mentioned areas, and one of the important reasons for this strong connection is the migration of nomads in the Fars plain and other highlands of Bakhtiari to these areas. The identified sites of this period, which were mainly in the form of temporary camps, also prove this claim.

Conclusion
In the Copper and Stone Age, we are faced with the dramatic emergence of yards in the Lordegan area. During this time, communication between the inhabitants of Lordegan and Fars and Khuzestan has increased. The reason for this claim is the collection of pottery that exists in this area. Another reason to prove this claim is the laboratory studies that have been done on the Lepui pottery of Chaharmahal and Bakhtiari province with Fars province. Based on the researches, it can be said that the inhabitants of Bakhtiari region have been influenced by the inhabitants of Fars and Khuzestan during the Copper and Stone Age. Given that most of the settlements in this area belong to the nomads, it can be said that this area has been a bridge between these areas during the Copper and Stone Age. Khosrozadeh also points out that the presence of pottery similar to late Neolithic cultural materials and copper and stone of Fars and Khuzestan indicates the strong connection of Farsan plain with the mentioned areas and one of the important reasons for this strong connection is nomadic migration in Fars plain and other heights. Bakhtiari knows of these areas, as the sites identified during this period, which were mostly temporary camps, also support this claim.

Abstract
Khuzestan, a primary center of mudbrick and fired-brick architecture in ancient Iran, witnessed the evolution of vaulted construction from the Elamite to the Late Sasanian periods. Among these, arched vaults served not only as structural elements but also as a demonstration of systematic engineering practices tailored to the region’s warm and semi-humid climate. Despite the abundance of surviving monuments, no comprehensive study has analyzed their technical and structural features to uncover the underlying stability principles. This study aims to examine the structural performance and recurring patterns of stability in arched vaults of Khuzestan. Field surveys, documentation of accessible structures, analysis of 111 identified vaulted buildings, and detailed examination of 21 selected representative examples were conducted. The study focused on the interaction of materials, geometric proportions, construction technology, and human craftsmanship in achieving long-term stability. Results indicate that vault stability depended on: 1) the type and geometry of bricks, consistent mortar thickness, and interlocking strategies; 2) diverse construction techniques, including corbeling, radial arrangements, and combination methods; 3) geometric proportions such as span, rise, and vault thickness; 4) adaptation to climatic conditions; and 5) the skill and experience of the builders. This research highlights the presence of a systematic engineering logic in pre-Islamic vault construction and provides a framework for restoration, conservation, and potential adaptation in contemporary architectural practice. The findings demonstrate that these vaults were not merely empirical or accidental in design but reflect deliberate, replicable, and coherent structural strategies.
Keywords: Structural Stability, Vaulted Architecture, Arched Vaults, Pre-Islamic Iran, Khuzestan.

Introduction
Khuzestan has historically played a pivotal role in the development of vaulted architecture within ancient Iranian civilizations. Vaults represent one of the most sophisticated elements of traditional construction, combining technical mastery, material understanding, and adaptation to environmental conditions. From the Elamite through Late Sasanian periods, vaulted buildings in Khuzestan reveal an evolution in construction techniques, reflecting the accumulation of knowledge and local innovation. Arched vaults, in particular, served as primary structural and functional components in ritual, funerary, administrative, and sometimes military architecture.
The study of these vaults provides insight into the strategies employed by ancient builders to achieve stability over centuries. Stability in traditional architecture encompasses not only physical durability but also cultural, climatic, and technical resilience. Builders utilized local materials, precise geometric proportions, and structured load distribution to respond to environmental and functional challenges. Despite extensive archaeological documentation, there has been limited focus on the technical principles underpinning vault stability, particularly in arched vaults.
This research addresses this gap by systematically analyzing recurring structural features, material properties, construction technology, and geometric patterns that contributed to vault durability. The study examines both historical continuity and the adaptation of techniques over time, demonstrating that pre-Islamic vaulting practices in Khuzestan were informed by deliberate engineering logic rather than trial-and-error. Understanding these principles is critical for bridging knowledge gaps in architectural conservation, informing restoration efforts, and inspiring contemporary applications of traditional construction methods.

Discussion 
Analysis of arched vaults in Khuzestan indicates that their long-term stability resulted from a combination of material selection, construction technology, geometric design, and human skill. Key aspects include:
Materials and Mortar: Builders employed trapezoidal, square, and rectangular bricks, wider and thicker at structural bases to distribute loads effectively. Mortars, including clay, gypsum, and bitumen, were chosen according to moisture conditions, ensuring cohesion and stability.
Construction Techniques: Techniques included inclined corbeling, radial arrangements, and hybrid approaches. Temporary wooden or reed supports facilitated precise execution, while multi-layer vaults with controlled thickness enhanced overall strength. Adjacent vaults were often coordinated to reduce lateral stresses.
Geometric Proportions: Ratios between span, rise, and thickness were carefully maintained across periods. Numerical proportional systems guided vault dimensions, while precise interlocking of bricks ensured efficient load transfer.
Human Skill: Mastery in aligning bricks, controlling mortar thickness, integrating vaults with walls, and designing stress-relief features such as recesses and buttresses reflected high craftsmanship.
The historical evolution from Elamite to Sasanian periods shows gradual refinement. Early Elamite vaults utilized simple rectangular cross-sections and limited brick types, while Late Sasanian vaults displayed sophisticated high-rise arches, modular brick use, and multi-layer arrangements. These developments indicate a cumulative knowledge system that informed construction practices and responded to functional and climatic challenges.
The study highlights that stability was never accidental; rather, it emerged from repeated, rationalized engineering practices. Such findings provide an empirical basis for restoration and reconstruction, enabling the preservation of architectural integrity and informing contemporary design strategies that draw upon historical methods.

Conclusion 
This research demonstrates that arched vaults in Khuzestan were underpinned by systematic engineering principles rather than empirical trial-and-error. Stability resulted from the integrated interaction of materials, construction technology, geometric design, environmental adaptation, and craftsmanship. The study identifies: 
- Strategic use of brick types and mortar selection to optimize structural cohesion.
- Refined construction techniques, including corbeling, radial arrangements, multi-layer vaulting, and controlled thickness.
- Geometric proportionality ensuring balanced distribution of forces.
- Adaptation to climate and environmental constraints.
- High-level craftsmanship in aligning elements and controlling structural behavior.
Historical analysis reveals a continuous technological development, culminating in Late Sasanian vaults that exemplify peak structural refinement. Documenting these features provides a foundation for preservation, restoration, and potential adaptation in modern architectural practice. Future studies may compare these vaults with contemporary structures in neighboring regions or explore the influence on early Islamic architecture in southwestern Iran.
The study confirms that pre-Islamic vault construction in Khuzestan represents a coherent, replicable, and sophisticated engineering tradition, offering valuable lessons for both conservation and contemporary design.