[493] Diversified trading networks have recently drawn a great deal of attention. In the process, the importance of diversity has perhaps been overemphasized. Using the trade in port wine from Portugal to Britain as an example, this essay attempts to show how a market once dominated by general, diversified traders was taken over by dedicated specialists whose success might almost be measured by the degree to which they rejected diversification to form a dedicated 'commodity chain'. The essay suggests that this strategy was better able to handle matters of quality and the specialized knowledge that port wine required. The essay also highlights the question of power in such a chain. Endemic commodity-chain struggles are clearest in the vertical brand war that broke out in the 19th century, which, by concentrating power, marked the final stage in the transformation of the trade from network to vertical integration.