Abstract – The analysis is based on a corpus of 1796 coins with an iron core (nummi subferrati), put together thanks to a collective investigation covering the provinces of Germania Inferior and Superior, Gallia Belgica, Lugdunensis, Aquitania and Narbonnensis, the Alpes Pœninae, Raetia, Noricum and Pannonia. The different quantitative approaches have enabled the identification of two phases of production separated by both location and time. Phase 1 occurred between AD 20/30 and AD 60/70 and essentially involved Gallia Belgica and the provinces of Germania. 88% of its output comprised Asses, copying types issued under Augustus and Nero. After a hiatus of still indeterminate length, but undoubtedly of almost a century, Phase 2 occurred, dated between c. AD 160 and AD 220 and characterised by the production of sestertii (50%). During the initial period it was located both in the north-west of Gaul and in the Danubian provinces, where it developed rapidly and vigorously. The production of bronze subferrati fell into disuse during the 230s AD and disappeared completely shortly after 260, this no doubt co-inciding with the appearance of cast forgeries in copper alloy, produced in large quantities thanks to a simpler technology.