The concept of "natural setting" should be taken to mean the state of the site before it was settled-even though it is sometimes difficult to distinguish the natural site from the Roman one.

Instead of reflecting a sort of frozen state, however, the concept should be somewhat qualified: the example of the Seine alone shows us that the Parisian landscape has always been changing.

In addition, perceiving this "natural" state is not made easy by the many changes made to the landscape up to the present day. The level of terrain has been reduced and raised up so much that the current topography gives a distorted image of the land in ancient times. In the same way, the riverbeds and banks of the Seine and the Bièvre rivers were very different from how they appear today.