E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
With silver weapons you may conquer the world, is what the Delphic oracle said to Philip of Macedon, when he went to consult it. Philip, acting on this advice, sat down before a fortress which his staff pronounced to be impregnable. You shall see, said the king, how an ass laden with gold will find an entrance.