Also another question: Was one of those cities Venice itself or was there an even financially stronger city in it's time?
Such trading, particularly futures trading, date far later than the period you're asking about. Futures trading is, I believe, often dated pretty specifically to the tulip mania in the Dutch Golden Age. It's not my period, so I'm afraid I can't go into great detail about the evolution of trade as we know it, but my understanding is that it dates from the 1600s. Hopefully someone can come in and provide more detail and correct any errors in what I'm saying.