Trading towns were critical to the dissemination of products along the Silk Road and Indian Ocean trade routes. Hangzhou, Timbuktu, and Malacca are a few examples of prominent commerce cities. All are conveniently positioned along important rivers, with several also along overland commerce routes. Commerce cities tended to be larger than other settlements, with an established commercial district along with satellite communities that grew up around religious sites or as defense against invaders. In addition to being major transportation hubs, many trading cities had significant political roles too. Indeed, some have gone so far as to say that all cities developed in antiquity were trading cities until the advent of Rome! Trade was vital to any city's survival - without goods to exchange for products from elsewhere in the world markets there would be no market for those products, and without buyers there would be no need to produce them. A city that controlled its own trade routes could therefore influence the supply of items that were available to buy and sell. Trading cities also played an important role in the spread of religion - many religions emerged or evolved in places where trade was concentrated such as Egypt, India, and China. In order to practice their beliefs, people needed commodities with which to decorate themselves or build shelters, so trade was essential to their culture too. The development of large urban centers was certainly not a new phenomenon when Europe began its expansion into the rest of the world.