The fact that stamps have to be placed before a vessel is fired means that the manufacturer is involved in the production process. Because of this it is likely they will have had a similar function as the maker’s marks. They could be applied to the wet clay easily (although the wares should not be disfigured while the stamp was placed), and a stamp could be used repeatedly before they would need to be replaced.

Another theory states that these stamps were part of the imperial control over trade, with the stamps denoting that an entire batch of amphorae was “approved” for commercial usage. There might be some merit to this idea of the “imperial” stamps, which could be related to the annonic tax system (indicating that the content was part of the due taxes of a certain region).

However, the smaller stamps are not likely to have had this function: they are more likely to have been maker’s marks, which could be used in a similar way as the graffiti. This also fits with stamps found in Ostia in Late Antiquity, where stamps indicate the manufacturer of the amphorae as well as the city of origin. This would also explain why the stamps are placed on the base of plates and bowls: as with the graffiti, they would not have to be visible; their presence on the object was enough.