Arches and vaults are complex structural systems whose structural behaviour is influenced by the geometrical arrangements of the structural parts and the mechanical nonlinearities due to the interaction between resisting blocks and contact layers. The latter can have either zero thickness (as in dry assemblages) or finite thickness (as in mortar joints). Different modelling techniques can be adopted within Finite Element Method (FEM) to assess the structural systems’ strength and displacement capacity. Micro- and macro-modelling approaches are the most widespread. Micro-models are based on the simulation of the interaction between bricks by means of interface contacts, which represent the mortar joints; conversely, macro-models assume that the masonry structural elements are a continuum solid with mechanical properties equivalent to those of the masonry assembly. Micro-models are typically highly computationally demanding, even though they allow a more detailed crack pattern identification. In contrast, macro-models are generally more efficient. This research considers the behaviour of a brick masonry arch under lateral loads that resemble a seismic condition. FEM models are developed to predict the response of the arch by comparing the accuracy and the computational efficiency of simplified micro-models with macro-models. The results provided by the two numerical approaches are compared and critically discussed, including an analysis of the limits and advantages of both techniques.