This paper offers a new reading of Heraclitus fragment B90 (Diels-Kranz). It argues that we can enrich our understanding of the fragment by reading it, not as a primitive analogy, but as a skillful simile grounded both in the poetic tradition and in the cultural context that would have conditioned its significance for Heraclitus and his audience. Read in this way, B90’s evocation of a cosmos whose common measure parallels the common measure of the polis’ marketplace is not simply a (...) source of cosmological doctrine. It is also an epistemic challenge that threatens to undermine the very possibility of cosmology. (shrink)