The starting point of this study concerns the origins of the polycentric nature of contemporary cities in the western area of the Netherlands, commonly known as ‘the Randstad’. Within the disciplines of planning and urban design the Randstad is considered a textbook example of a polycentric urban hierarchy. Yet, although quite a popular topic, very little is actually known about the driving forces that have given shape to existing urban hierarchies throughout the world. Moreover, the Randstad has also been dubbed ‘Holland’s paradox’ because of its assumed reversed evolution from a primate city hierarchy focused on Amsterdam in early modern times, to a polycentric hierarchy in the 19th century. Why do urban hierarchies change over time and which factors were decisive for the rise of the polycentric Randstad? Expansion of Haarlem, Amsterdam, Leiden, Den Haag, Gouda, Utrecht, Delft, Rotterdam en Dordrecht. This map was produced as a part of the Mapping the Randstad Holland-project and was published before in Borger, G.J., et al. (2011). Twaalf eeuwen ruimtelijke transformatie in het westen van Nederland in zes kaartbeelden. Overholland, (10/11). This study consists of two parts and six chapters. Part I explores the determining factors of change within urban hierarchies. The first chapter gives an assessment of the usefulness of existing theory and ends in confusion: firstly, historiography turns out to be a medley of explanations that are heterogeneous and sometimes even contradictive. Secondly, comparisons of the long-term development of multiple towns are lacking, which makes it difficult to come up with a theoretical approach. In order to make such comparisons and ascertain the impact of certain factors on urban hierarchies over time, it’s necessary to look at the development of a group of towns over a long time-span. Therefore, in the second chapter, simple statistics are compared with existing theory and literature. To do so, demographic data for the nine towns of Amsterdam, Haarlem, Leiden, Delft, The Hague, ...