Abstract
The ancient city of Bam, one of the five main cities of Kerman Province in southeastern Iran, developed based on a three-part structure: the governorate (citadel or Dezh), the commoner quarter (Shahrestan), and the suburb (Rabaz). Within the defensive walls of the Shaherstan, numerous troglodytic spaces exist. A study of 162 troglodytic spaces within the defensive wall of the Arg-e Bam revealed the necessity to study the reasons for their formation, development, and chronology. This research addresses questions regarding the characteristics of the troglodytic spaces, the factors influencing their spatial structure, and their chronological evolution. Through field surveys and documentary analysis, this study identifies architectural features, analyzes structural influences, and determines construction methods and their dating. Results indicate significant diversity in floor plans, spatial geometry, elevation levels, arch shapes and height, and structural composition (clay layers vs. mud-brick combinations). Key factors influencing these spaces include the city’s geographical and historical context, traveler volume, location relative to the main southern gate, wall materials, usage patterns, and the relationship between ceiling height and floor elevation. While the initial phase of the Arg-e Bam wall dates back to the Seleucid period or early Parthian era, the excavation of the first troglodytic spaces likely occurred concurrently or shortly thereafter, during the Parthian or Sassanian periods. However, written sources and evidence of defensive wall reconstructions during the Islamic era suggest that the creation and development of these troglodytic spaces continued from the early Islamic period up to the late 18th century AD. 
Keywords: Islamic Architecture, Vernacular Architecture, Arg-e Bam, Troglodytic Architecture, Defensive Wall, Hesar.

Introduction
Troglodytic architecture reflects the technical and artistic skills of its creators, as well as the cultural beliefs of different socities. Beyond residential functions, these spaces served as social, religious, and economic hubs. This architectural style demonstrates human adaptation to the environment and the optimal use of local resources, allowing for harmonious integration with natural surroundings (Abdel-Azim & Osman, 2018). Features such as thermal and moisture insulation enabled inhabitants to thrive in harsh climatic conditions by maximizing natural resources. While troglodytic architecture in mountainous regions typically takes the form of deep caves, in plains, it manifests as tunnels and surface chambers. 
The defensive wall of Arg-e Bam contains numerous diverse troglodytic spaces. The issue of this research is the existence of such troglodytic spaces in the “wall texture”. Because troglodytic spaces in the clay texture of defensive walls of cities have rarely been reported. The only introduced case is found in Narin Qal’eh of Meybod, which features a clay (Chineh) and mud-brick defensive wall structure (Nikzad & Ghafouri, 2015: 111).
The objective of this paper is to document and conduct statistical studies, morphology (physical and structural characteristics), architectural elements, construction methods, and dating of the troglodytic spaces in the Arg-e Bam defensive wall, while explaining their evolutionary development.
The research method combines field surveys and documentary studies. Theoretical dimensions, research background, and geographical and historical characteristics of the studied area were compiled through documentary methods. Field surveys were conducted to supplement documentary information, document architectural features, and identify specific elements. Statistical analyses were conducted based on the variables and architectural features of the troglodytic spaces. 

Discussion
Field surveys of the defensive wall of the Arg-e Bam after the 2003 earthquake identified over 240 troglodytic spaces for the first time. However, many were destroyed, leaving only traces. In the second phase, 162 intact spaces or those revealed during debris removal were documented. Spatial distribution shows the highest concentration in the southern wall (63 spaces), followed by the western wall and Konari-Mahalleh (53 spaces), the eastern wall (37 spaces), and the northern wall (7 spaces). These spaces range in size from 1 to 10 square meters, with one exceptional case measuring 15 square meters.
The troglodytic spaces of Arg-e-Bam are divided into rectangular (or square) and curved groups based on their plan. Most curved spaces lack regular or specific designs. There are 66 rectangular spaces and 96 curved spaces. This predominance of curved, irregular shapes suggests a process of population growth and urgent needs that led to the organic development of spaces without pre-designed plans.
In terms of spatial geometry, the troglodytic spaces are divided into single-chamber (122 cases), two-chamber (35 cases), and multi-chamber (5 cases). The prevalence of single-chamber cases indicates that subsequent changes and developments likely led to the formation of additional spaces around or along the axis of the original space (centripetal or longitudinal expansion).
The troglodytic spaces are located at various elevations: some are above ground level, some are flush with the surrounding land, and one is excavated below ground level. Notably, the western wall and Konari-Mahalleh exhibit a significant increase in the use of mud-brick compared to pure clay (Chineh). This shift is likely related to the need for a higher ceiling and improved structural stability. Statistical analysis of spatial location reveals that the highest density of troglodytic spaces is in the southern wall. Due to its proximity to the main entrance and market, this area features more spaces designated for temporary residential use and production workshops.
Given that the initial formation of the Arg-e Bam defensive wall dates to the Seleucid or early Parthian era, the excavation of the first troglodytic spaces likely occurred during the Parthian or Sasanian eras. However, written sources and evidence of wall reconstructions and destructions during the Islamic era indicate that the creation and development of these spaces continued from the early Islamic period through the late 18th century AD.

Conclusion
The analysis of structural and spatial elements of the Arg-e Bam defensive wall highlights significant diversity among the troglodytic spaces. The frequency of curved plans compared to rectangular ones probably represents a developmental process driven by population growth and practical needs, resulting in irregular, asymmetrical shapes without pre-designed layouts. Structurally, while single-chamber cases are the most common, subsequent modifications led to an increase in two- or multi-chamber configurations, where new spaces were formed around or along the initial cavity.
Although most troglodytic spaces were dug into the clay texture of the defensive wall, and the number of spaces dug in the mud-brick texture of the wall is less, the use of mud-brick is significant in the western wall and Konari-Mahalleh, and the reason for this should be related to increasing the height of the ceiling and improving the structure. Some mud-brick elements predate the excavation of the troglodytic spaces and were exposed by clay layer collapses, while others were added later to reinforce walls.
Statistical analysis confirms that the southern wall has the highest density of troglodytic spaces, where, due to its proximity to the main gate and the market, more spaces with temporary residential uses and workshop spaces have been created. The height of the ceilings in southern troglodytic spaces is shorter, and their space is more limited, indicating rapid creation and temporary uses. In contrast, higher-elevation spaces in the western wall have more regular plans, suggesting more diverse and stable functions.
Based on archaeological and laboratory evidence, the defensive wall’s initial formation dates to the Seleucid or early Parthian era. implying that the first troglodytic excavations occurred during the Parthian or Sasanian periods. However, based on written sources and the process of reconstruction and destruction of the wall during the Islamic era, it seems that the creation and development of troglodytic spaces continued from the early to the late Islamic period (late 18th century AD). Comparative studies with regional troglodytic spaces (from the Afraz and Bagh Chammak fault areas) and trans-regional cases (such as Samen and Narin Qal’eh in Meybod) support a formation date from the late Parthian to early Sassanid period for the Bam troglodytics. While their development occurred between the early Islamic period and the late Islamic centuries. In general, the troglodytic spaces of the Arg-e Bam historically represent a continuous process of cultural and social development and diverse uses throughout the history of this complex.