The paper presents a preliminary seismic assessment of the Temple of Madonna delle Cataste in Ponzano di Fermo, central Italy. According to the farmer who built the temple starting from 1921, an apparition of the Virgin Mary happened above a stack of wood (hence the toponym in Italian). The Temple -which stands unfinished and without a roof- is built in one story, octagonal in plan, with all eight façades allowing access to the centre by arched entrances. The polycentric arches show a horseshoe profile. Upon initial visual analysis, little damage appears on the structure, i.e., erosion and biological staining. The municipality has recently opened an architectural competition aimed at the functional reuse of the structure, which also implies a seismic assessment. Here, the safety of the structure will be preliminarily verified using a recently developed procedure that exploits a heterogeneous Distinct Element Upper-Bound Limit Analysis formulation. The structure is discretised with rigid hexahedral (macro)blocks joined by elastic perfectly plastic interfaces, loci of power dissipation. A Mohr-Coulomb failure criterion with tension and compression cutoff is assigned to mortar joint interfaces. The Limit Analysis formulation is implemented in a homemade script in MATLAB and provides the maximum horizontal acceleration the structure can withstand, the interface plastic multipliers and the failure mechanism. In view of the insufficient horizontal load-carrying capacity, a seismic upgrade is proposed, with a steel belt installed at the top crown, and its efficacy numerically evaluated.