This article examines the development of medieval cities in Northern Germany by focusing on the operation of their marktplaces. In the first section, I explore how villages, towns, and marketplaces evolved spatially into cities in terms of topography. In these areas the center of towns was composed of rulers` citadels(Burg), residential places of long-distance traders(Wik), and marketplaces. Early cities retained not only defense facilities and military centers represented by lords` castles(Luniburc), bishops` citadels(Domburg), and kings` residence(Palatium), but also marketplaces whose function was quite different from that of other. The function of marketplaces was initially undertaken by Wik that was directly Linked to long-distance trade routes, but the trading posts(Wik) did not lead in developing marketplaces into cities. As urban population, industries, and the center grew gradually, the necessity for trading also increased in surrounding regions as well as at a long-distance. Simultaneously merchants and artisans began to settle the newly growing cities. As the function of marketplaces became active, they closely linked many villages that had already existed, and especially played a crucial role in providing non-agricultural population with living necessities. While functionion as the center of regional trade satisfying "the internal demand" rather than long-distance trade aiming at luxury goods, marketplaces took more decisive steps to establish themselves as cities. Along with such development of cities, marketplaces witnessed dramatic spatial expansion. Commercial aspects of medieval cities in this region are recognized as the most essential one, although they are not necessarily peculiar compared to the cities in other regions and periods. It is because the active function of marketplaces largely affected not only their growth into cities but also the subsequent urban development. Marketlaces were located topographically in the central part of cities and strategic points of transportaion because the cities in their formative stages grew out of marktplaces, the center of trade and business, and accordingly other urban facilities and residential places also came into existence surrounding marketplaces. When the activities of marketplaces formed and indispensable element in their development into medieval cities, then what gave rise to active function of marketplaces? Preious literature based on limited existing sources mainly pays attention to kings` role and auhority by emphasiizing legal aspects including charters for marketplaes. For instance, it has been admitted that the Otto Empire organized Imperial Church System(Reichskirchensystem) by pursuing a consistent policy of charters for marketplaces. However, other cases like in Hildesheim show quite a different picture in which competent urban lords were able to achieve economic gains and urban development without charters. Aside from kings and urban lords, merchants and artisans were equally essential agents in building the cities, even though they were hardly conspicuous in written sources and if any, only in a passive manner. There are few adequate materials that illustrate their activeites especially in the early phase of urban formation. But later, for instance, around the 13th century we can see a very different scene in which city dwellers (merchants and artisans) made the most of their economic capability and newly enacted urban regulations in order to secure equal and even superior status against lords in taking the initiative in marketplaces. In sum, city dwellers were able to control the cities, especially marketplaces together with urban lords and their agents.