Limit analysis is a commonly used method in the assessment of masonry constructions. This article deals with the use of limit analysis in order to study the equilibrium conditions during the intermediate building stages of the Gothic apse in Tortosa cathedral (1345–1441). This analysis is typically used in completed structures, but its use in the intermediate building stages may provide relevant data beyond the existing historical information. The design of this heptagonal apse entails a greater calculation complexity than the cathedral’s central body. Besides, the intermediate building stages generate asymmetry situations at the pillars. The results obtained shall enable us to determine the building stages in which the structure’s equilibrium may have been endangered, and therefore a temporary thrust countering system was required. Two different graphic statics strategies have been used. These strategies are based on the same principles, but imply a different degree of simplification.