These are problems that cannot be solved here, obviously. But they have to be borne in mind as we proceed. For the fact of this economic expansion is of essential importance if we want to understand the whole dynamic of medieval society in these central centuries, and indeed later; but when it is explored here, it must be recognize how far basic data and interpretations are missing. Some general points are clear: the fact that Paris and the Paris basin became unusually economically active in the twelfth century, for example, is a basic context for the growth of the Paris Schools and, later, university (for there was no point attracting students if there were no infrastructure to feed them) as well for the capacity of Philipp II of France, with only a restricted territory under his direct control, to match the resources of John of England in their wars in the early thirteenth century, and also for the concentration of resources which produced the striking density of very expensive new gothic cathedral in every city of northern France. But, having said that, we must be honest and admit that we do not really understand how the economy of the Paris region worked in this period