—Ian Lindberg (Mentor: David Bachrach)


During the summer of 2022, I set out to research these siege engines with the support of a Summer Undergraduate Research Fellowship (SURF). To make an accurate assessment, I needed to analyze them from an engineering perspective, as siege engines can be viewed as a kind of machine, limited by all the same engineering and physics principles as any modern machine would be today.

As someone pursuing a major in mechanical engineering and a minor in history, I was ideally suited to interpreting the descriptions of siege engines as presented in historical texts. The ultimate goal of this research was to identify siege engines from historical texts, create plausible designs for them, then turn these designs and the justification for them into a form useful for historians studying this period.  At the time of the writing of this research article, I have been able to use the descriptions provided in the sources along with supplementary materials, including academic papers, to create a 3D model of a siege tower. By using engineering methods and software, I was able to make this model both accurate to descriptions provided in sources as well as capable of being used in the manner described in the sources.

Ian Lindberg

Ian Lindberg

Preliminary Research: Identifying and Describing Siege Engines

My research began by investigating English translations of primary and secondary accounts of the First Crusade, such as the Gesta Francorum, Ralph of Caen’s Gesta Tancredi, and Anna Comnena’s Alexiad (Hill, Hamilton et al., Comnena and Sewter). After selecting sources, I acquired them in a mix of print and digital formats through the Dimond Library at the University of New Hampshire. I read through each source and transcribed passages which described siege engines and their use. With one document for each source containing the transcribed passages, I went back through these documents and summarized the descriptions provided in accounts, then added my own comments regarding the feasibility of these engines when viewed from an engineering perspective.

I then created one document for each type of siege engine mentioned in the sources, which were: stone throwers, siege towers, or rams. I combined the descriptions from the various sources to create composite descriptions of each of the three major types of siege engines used in the First Crusade. All three of these types of siege engines served unique purposes within the greater scope of a siege. Stone throwers hurled stones or other objects to attack defenders and damage defenses, rams broke down gates and punched holes in walls, and siege engines protected attackers and brought them to the tops of walls during the final assault. Source descriptions used for these composite descriptions included mentions of several dozen individual siege engines of all three types used in the four major sieges of Nicaea, Antioch, Ma`arrat Al-Nu`man, and Jerusalem (Hill).

In just the preliminary process of reading through sources and extracting sections which contained descriptions of siege engines, I was able to identify the use of certain sub-types of siege engines, such as stone-throwers operating with a torsion mechanism, which were previously not thought to have been in use during the First Crusade. Previous academic work on the First Crusade has concluded that machines of this type did not appear until later in the 12th century, so my identification through an engineering perspective of these machines being used in combat before 1100 is significant.

Siege Towers and Their Importance

After reviewing my composite descriptions of stone throwers, siege towers, and rams, I decided to focus on an in-depth analysis of siege towers, as there was a large amount of information provided by the sources describing them in comparison to other siege engines, likely due to their importance in successfully undertaking sieges. The importance of siege towers in the success of the First Crusade and the lack of existing research on them also made siege towers a logical choice to conduct further analysis. Working from the composite description I had previously created, I began to create engineering sketches of possible designs, including dimensions and several views including cross-sections, which would match those used in the First Crusade. In addition to directly using the details on size provided by the sources, I also accounted for the scale of the fortifications which the siege towers were being used against. To do this, I consulted with my mentor, Dr.David Bachrach, of UNH’s History Department, on the nature of the fortifications, and he was able to point me to archaeological studies such as one conducted on the remains of the walls of Nicaea that shed light on the scale of Near East fortifications as they would have existed in the late 11th century (City Walls in Late Antiquity). With overall dimensions and a tentative design, I then moved to modeling the siege tower in SOLIDWORKS, an engineering 3D design software.

Lindberg Siege Tower

The model of a siege tower built by the author in SOLIDWORKS.

Beginning in SOLIDWORKS with a basic design I derived directly from my initial sketches, I gradually refined the design to be more detailed and realistic. As part of the refinement process, I discussed fabrication methods with Dr. Bachrach, and he was able to provide me with academic papers detailing methods of joining the wooden beams that were used in Western Europe during the time of the First Crusade (Hewett). I then incorporated these specific methods into the SOLIDWORKS model. I also incorporated the availability of beam sizes cut from trees of types mentioned in the sources and those that would have been growing in areas near where the sieges took place. Once I had reached a realistic model that matched the descriptions provided by the sources and other supplementary information, I incorporated the material properties of timber, such as density and strength, likely to have been used in the construction of these siege towers. I also used SOLIDWORKS Simulation FEA software to subject the model to realistic loading conditions as it would have seen during the First Crusade. The loading conditions considered included the weight of soldiers inside and on the siege tower, as well as the forces the tower would have experienced while being rolled into battle.

Using the results of these SOLIDWORKS simulations, I further refined the model of the siege tower until I reached a design that fulfilled the descriptions provided by the historical sources and stood up to rigorous inspection through engineering analysis methods such as computer simulations of realistic loading conditions using finite element analysis, a computational method. This combination of factors into one design meant that the siege tower would match the source descriptions in both visual appearance and functional capabilities in combat.

Significance of This Research

The research I conducted this past summer with SURF support is significant in several ways. From the perspective of historians interested in the First Crusade, my research investigated the use of siege engines in a depth that has not been done before. Analyzing siege towers specifically, which my research found to be crucial in Crusader victories, is an area in which no major research has been conducted before, as other research on siege engines focused primarily on stone- and bolt-throwing engines.

My background in engineering and ability to apply knowledge, methods, and engineering software to this topic allowed me to create a realistic and accurate model of a siege tower which someone without my background would not have been able to. I hope that the results of my research will be able to serve as a reference for historians and others interested in this topic who do not have an engineering background. I feel that the results of my simulations and visual media will also allow historians and others interested in my work to understand these machines and the First Crusade in a new and interactive manner. Additionally, I hope the interdisciplinary nature of my research will provide a template for future collaboration between engineers and historians. Only a few people, including myself, have conducted research that combines engineering with medieval history, and there is great potential for future work of this type.

Future Plans

In the near future, I plan to continue working on my model of the siege tower to further refine it using simulation results. I also plan to create drawings and renderings from my 3D model as visual aids to help convey the results of my research to historians. Additionally, I plan to continue with the process of turning the work I have completed so far into a written form that can be understood without an engineering background while also including enough information for a reader with a background in engineering to understand my methods. When this is completed, I hope to present my research at a conference outside of UNH and possibly pursue publication in a journal such as Technology and Culture. I would also like to continue my analysis on other types of siege engines used in the First Crusade and turn the results of my research into a form which is accessible for historians and others without an engineering background.

Beyond the scope of this project, I hope to continue combining my interests in engineering and history, and possibly extend the scope of my research to other time periods. Being given the opportunity to conduct this research with a SURF has been an incredible experience. Engineering and history have long been my two greatest areas of interest and combining them in an academic context allowed me to apply and gain better understanding of both areas. Within the discipline of history, this research enabled me to become more experienced and effective in identifying and analyzing period sources. Within the discipline of engineering, I gained experience and became more adept at applying my education and skills to solve abstract challenges. I feel that the experience of interdisciplinary research will enable me to be more successful in my future research, both interdisciplinary and otherwise, in graduate school and beyond.


Conducting this research has been an incredible experience. It has allowed me to combine two of my areas of interest and study in a project that I never expected I would have the ability to pursue. I would like to thank Dr. Bachrach for his invaluable assistance and expertise in navigating and interpreting medieval sources and his willingness to take on a rather unconventional project.  I would also like to thank those who made funding possible for my project through a SURF grant from the Hamel Center possible, including Mr. Dana Hamel, the Rogers Family Undergraduate Research Fund, and the Donald J. Wilcox Endowed Fellowship Fund.



Asbridge, Thomas. The First Crusade, A New History. New York: Oxford University Press, 2004.

City Walls in Late Antiquity. Oxbow Books, 2020. https://doi.org/10.2307/j.ctv138wsz8.

Comnena, Anna, and E. R. A. (Edgar Robert Ashton) Sewter. The Alexiad of Anna Comnena. The Penguin Classics. Baltimore: Penguin Books, 1969.

Hamilton, Professor Bernard, Dr David S Bachrach, Professor Bernard S Bachrach, Professor Peter Jackson, Professor Norman Housley, Professor Peter W Edbury, and Professor Malcolm Barber. The Gesta Tancredi of Ralph of Caen: A History of the Normans on the First Crusade. Vol. 12. Crusade Texts in Translation. Ashgate, 2005.

Hewett, Cecil A. “Structural Carpentry in Medieval Essex.” Medieval Archaeology 6, no. 1 (January 1962): 240–71. https://doi.org/10.1080/00766097.1962.11735668.

Hill, Rosalind, ed. The Deeds of The Franks and the Other Pilgrims to Jerusalem. New York: Oxford University Press, 1962.

Ibn al-Qalānisī, Abū Yaʻlá Ḥamzah ibn Asad, and H. A. R. (Hamilton Alexander Rosskeen) Gibb. The Damascus Chronicle of the Crusades. University of London Historical Series, No. 5. London: Luzac, 1932.


Author and Mentor Bios

Ian Lindberg is from Hampstead, New Hampshire, and will graduate in spring 2023 with a bachelor of science degree in mechanical engineering and minors in history and computer science. He is also in the University Honors Program in the interdisciplinary track. After taking Professor Bachrach’s course on medieval military history, Ian was inspired to undertake this interdisciplinary Summer Undergraduate Research Fellowship (SURF), which he is now continuing for his Honors thesis. Ian rose to the challenge of using sources from nearly a millennia ago to create 3D models using today’s engineering software. According to his mentor, this approach is incredibly unique to the historical field. He hopes the project and his research process itself will serve as a model for other kinds of innovative, interdisciplinary undergraduate research projects. Ian plans to pursue a master’s degree in mechanical engineering with the goal of creating new medical devices. This research has also served as preparation for a career in the medical field which is inherently interdisciplinary as well.

David S. Bachrach has been a professor in the History Department at the University of New Hampshire since 2001. He specializes in medieval European history, with a focus on the military, governmental, and administrative history of the kingdoms of Germany and England. Dr. Bachrach teaches broadly across medieval Europe as well as offering world history courses that focus on beer and warfare. He met Ian as a student during his class on medieval warfare and became Ian’s mentor for his Summer Undergraduate Research Fellowship (SURF) project. Ian’s approach, as a mechanical engineering major, brings an entire palette of skills to the study of medieval siege engines and Dr. Bachrach learned an enormous amount from working with him. Dr. Bachrach has mentored undergraduate researchers and authors for Inquiry before and finds it important to be able to communicate the significance of historical research to a broader audience. Especially for an interdisciplinary project like Ian’s, the novelty of bringing together engineering and history can lead to important new discoveries. 


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Copyright 2023, Ian Lindberg