The Survey of Module in Achaemenid Architecture, Case Study:The Palace of Apadana and the Hall of a Hundred-Column

Achaemenid era is the heyday of culture and civilization in which art and architecture make remarkable advances. Relying on other civilization’s legacy, Achaemenid architecture developed a distinguished and rather complex module which consists of the application of hidden grids and brick-based modules which were adopted by their neighbors prior to Achaemenids. This paper focuses on the survey of Achaemenid architectural module in Persepolis. Applying the descriptive research method, this research has been complied with the help of documents, maps and field surveys, meanwhile, the data has been analyzed by using Matlab and AutoCAD software. This article tries to respond to such questions, including: the basis of Achaemenid module formation, the extent of Achaemenid inspiration from other common module systems and the survey of common modules in The palace of Apadana and the hall of a hundred-column. According to the results, it is apparent that Achaemenid module is based on the dimensions of the bricks (standard brick of 33˟33˟13 cm) thereby, forming a brick-based module. In addition, this module seems to have been adopted from Babylonian brick-based modules and has been well inspired by Geek length measurement systems. This feature can align to the combinatorial nature of Achaemenid architecture. Moreover, two common modules in these two palaces are Cubit and Royal Cubit, which are thoroughly based on the human body dimensions. It is also noteworthy to mention that the adoption of each module depends on the application of that structure. Another valuable finding of this research is the numerical correlation between modules which seems to follow the same pattern of neighboring systems such as Greek and Babylonian modules. The result of this research rejects the suggested modules by Michael Roaf and Freidrich Krefter.

Introduction
Having met one of the most fundamental needs of human being, shelter and security, architecture evolved into a more complex system consisting of geometry, proportion and module. Among all these factors, Module seems to be the least known aspect of Iran’s pre-Islamic architecture. Module, in architecture, is an arbitrary unit adopted to regulate the dimensions, proportions, or construction of the parts of a building. Unfortunately, there are certain ambiguities surrounding the formation and evolution of the pioneer module system in Iran’s architecture. The process of its formation, origin or the impact of module systems of neighboring civilizations is not determined yet. Moreover, the existence or absence of different module systems in different regions of Iran or even the continuation of an initial module system of the historical period in Islamic period are questions that have not been answered yet. Knowing that primitive forms of module including, length measuring units were used in Sumer, Egypt, Assyria, India and Greece would raise the question whether there had been a distinct module system in Iran or not. Therefore, any attempt to uncover the evolution of a module in the architecture of pre- Islamic Iran would be worthwhile. To this end, the remarkably intact remains of Achaemenid stone architecture are proper samples to be studied compared to previous periods. This paper focuses on the survey of pre-Islamic modules particularly in Persepolis. Applying the descriptive research method, this research studies the architectural remains through two distinct approaches, including mere mathematical studies and analysis of defining measurements in each structure and the second approach consists of applying griddings as well as mathematical analysis. Each approach is examined thoroughly and the results are demonstrated, however; the first one seems to be utterly inadequate since it provides incongruous data within different units of a single structure, meaning each unit’s module seems to be different from the neighboring unit which is unreasonable. Consequently,  Discovering the modules in Persepolis was made by drawing grids on the outlines of the plan and dividing the grids based on the standard distance between column axes. Therefore, column axes and other defining parts of the buildings for instance, the stone walls and gates had to correspond to the suggested module. Each grid is a square of 33.34˟34 cm which remarkably overlays the existing outlines of the plan and informs us of the adoption of girds while designing the plan of Apadana and The hall of a hundred-column. The overlap of the aforementioned grids with the outlines is so precise that if the Apadana map was plotted separately with these grids and placed on the current plan, they would overlap to a great extent.
 
Identified Traces
According to the results, it is apparent that Achaemenid module is based on the dimensions of the bricks (standard brick of 33˟33˟13 cm) thereby, forming a brick-based module which was inspired from Babylonian brick-based module. The use of this type of module can be traced back to late Babylonian architecture and the site of E-Sagil. Given that Achaemenid clay bricks were made by the Babylonians, it is possible that the Babylonian brick-based module system may have influenced the Achaemenid architectural system, albeit not in size or dimension, since results demonstrate that the values of Achaemenid measuring units are influenced by their Greek counterparts. The brick foundation of all walls of Apadana, the hall of a hundred-column and the corresponding size of each brick with suggested module values, accredits the assumption that brick-based module might have been vastly used while constructing the buildings. This would have allowed architects to scale the dimensions of a building project by counting bricks without using a measuring rod. The Greeks adopted the Egyptian measuring system and made minor changes. This would better explain the origins of the Achaemenid measuring system and the correlation between aforementioned modules. It would also trace back the origin of the Islamic prominent modular system to a much earlier period. Once again such results can reveal the origin of Islamic prevalent grid plannings. Another rewarding finding of this study is identifying the differences between the commonly used modules in different buildings of Persepolis. There seem to be two different types of modules which have been adopted in Achaemenid architecture as Royal and common modules. Each module is compatible with special needs in Persepolis. In short, two common modules in the palace of Apadana and The hall of a hundred-column are Cubit and The Royal Cubit, which correspond to the size as well as the application of each building.
 
Conclusion
In conclusion, the Achaemenid module system is a combination of Babylonian brick-based module and Greek units of length measurement. The construction was conducted with the help of the Egyptian plan grids. Thus, it can be claimed that The Achaemenid architect used gridding plates, where each square served as a module,in order to design the palaces. The use of these grids has been very common in Egyptian architectural design. It is also likely that the Islamic gridding system may be a continuation of the pre-Islamic period.  Thus, what is seen in Persepolis is a combinatorial yet distinct tradition among all neighboring civilizations. It is worth mentioning that the prevalent Islamic period module has a rich history in Iranian architecture and seems to be the result of many years of Iranian architects’ experiences. It should be noted that the results of this study decline earlier studies conducted by Michael Roaf and Friedrich Krefter, despite their valuable efforts. Since the results demonstrate a logical and numerical relation between length measuring units in Achaemenid architecture. In other words, Royal Cubit, which is 66.68 cm seems to serve as the base of all modules. By dividing it into smaller amounts, one would obtain numbers which are other possible modules. The numbers obtained from these divisions are also present in the gridding plans and have a relative advantage over other numbers.