The neuter substantivecentenariumappears in a series of documents to designate a particular type of building. The etymology and precise meaning of this word have long been debated by scholars, who have proposed a wide range of explanations, none of which appears to be entirely satisfactory. In this paper, we put forward a different solution, taking into account textual, archaeological and linguistic evidence. In our opinion, the wordcentenariumcomes fromcentenum, which means a kind of a cereal; thus,centenariumindicates a ‘fortified grain-house’. It seems probable that originalcentenariawere military structures of varying shape and size, first created in the third century and then spreading in the Tetrarchic period. They appear to be distinctive of the African provinces, from which comes most of the evidence, but one cannot exclude that the same name was applied to similar structures in other parts of the Empire (such as in the Iberian Peninsula, for instance). The militarycentenariawere later imitated by private landlords – maybe even indigenous chieftains in charge of the defence of sectors of the frontier – who transferred the name to their unofficial or para-official defensive structures. This process of emulation was already advanced in Constantinian age.