<p>Although sandstone grottoes preserve invaluable heritage, the influence of ceiling geometry on their structural stability remains unclear. In this study, four representative grotto models with different ceiling types were developed using the discrete element method (DEM). Stress redistribution during excavation was analysed, revealing that the flat ceiling exhibits a cantilever-like response once the excavation front reaches the midpoint. When the ceiling is optimised into domed, vaulted or coffered types, the arching effect becomes progressively more pronounced, reducing cantilever-like bending and alleviating stress concentration at the rear wall by promoting more continuous compressive load transfer. Principal stress and factor of safety analyses further confirm this mechanism. This study introduces three conceptual models linking stronger arching action to greater confinement and reduced midpoint cracking. These findings establish a mechanics-based framework for assessing grotto stability and designing conservation measures in light of ceiling diversity.</p>