The corrosion mechanisms of a Roman iron bezel ring were investigated by in-depth characterization of its uncommon corrosion pattern and thermodynamic modelling. A silver foil and altered glass remnants were identified, covered with thick strata of magnetite and goethite. Underneath it, was a multi-millimetric cavity, filled with spheroidal magnetite or magnetite/goethite nodules in a siderite matrix. The bottom of the preserved object showed a marbled corrosion structure composed of goethite, magnetite/maghemite and hematite. Heterogeneous and evolving local conditions, involving synergistic effects of electrolytic and dissolution/precipitation mechanisms might explain the unique morphology and nature of the corrosion products observed.