The importance of terrain in warfare has often encouraged an intense relation between military conflicts and the use of techniques designed to understand space. This is especially relevant since the modern era, where the engineers who built and assaulted city defenses recorded the events with diverse documentation, including reports, diagrams, and maps. A large number of these sources contain spatial and temporal information, but it is difficult to integrate them into a common research framework due to its heterogeneity. In this context, geographical information science provides the necessary tools to explore an interdisciplinary analysis of these military actions. This article proposes a new approach to the study of sieges using a spatiotemporal formal model capable of integrating cartography, archaeological, and textual primary sources and terrain information. Its main aim is to show how concrete research questions and hypotheses can be explored using a formal model of this type of historical events. The methodology is applied to a particular case study: the French–Spanish siege of Barcelona that occurred in 1714. The protagonists faithfully recorded the development of the action, providing essential information for the model. Besides, different authors depicted the event as the paradigm of a city siege. For this reason, the model is also used to explore why real actions deviated from theoretical guidelines, clearly defined in different manuals. We use this scenario to explore two issues: (a) why the attackers chose to assault a particular city sector and (b) the factors that explain the casualties of the besiegers. We conclude that we need methodological tools capable of integrating heterogeneous information to improve the understanding of siege warfare that affected not only military conflict but also the shape of European urban landscapes.