The restoration of metallic archaeological artefacts needs the knowledge of ancient materials - their composition, their state of conservation and their manufacturing process - to avoid any inappropriate action in the restoration process. This paper is devoted to the study of a lead gallo-roman sarcophagus, found in a much corroded state after a long burial in a calcareous soil in the banks of the Rhone River at Lyon ( France). From the metallographic observations, it was found that the lead sheets constituting the sarcophagus have been directly cast on a table covered with a bed of sand. In addition, the presence of a thick corrosion layer consisting of lead oxide, lead carbonates and some important penetrations of PbO in the metal explain the loss of lead ductility and the important brittleness of this ancient material. The mechanism of formation and growth of this PbO layer in a carbonated medium was studied using electrochemical experiments and metallographic observations. Finally, the comprehensive study of this complex material consisting of lead metals, a PbO/lead carbonate layer and some compounds of the soil allowed the setting up of a restoration process based on an electrochemical reduction method. (C) 2004 Kluwer Academic Publishers.