The genius who realised that gunpowder could be used as a propellant remains unknown. All we do know is that the first illustration of a piece of ordnance occurs in a treatise by one Walter de Millemete entitled De Officiis Regum (On the Duties of Kings). Dated 1326, it is preserved in the library of Christ Church, Oxford. The gun was called a vaso from the Italian for a vase which it closely resembled. England lagged behind the rest of Europe in gun-making during the 14th century. Judging from the name vaso, Walter's gun was probably made in Italy which led Europe in metal-working at that time.