The study of archaeological analogues is a helpful tool to asses long-term corrosion behaviour for a wide range of materials. In this work, a celtiberic belt-buckle is studied as analogue for a composite material of carbon steel, bronze and a final coating of magnetite, also providing a hypothesis about the ancient fabrication of these coatings. The paper goes through a metallographic examination of the sample and compares the corrosion phenomena suffered with those of two other metallic objects, recovered from the same archaeological site. It includes geochemical analysis of the soil from which the reference objects were recovered. The belt-buckle, after being cremated and buried over two millennia into a rather aggressive environment, showed remarkably high resistance against corrosion.