For many years, the excavations of Iron Age and Roman sanctuaries provided the opportunity to analyze the pollen found in their infills, with a view to drawing up a picture of the surrounding vegetation. Here we suggest a new interpretation of the former data from the North of France and Belgium. Our present corpus brings together eight intra-site studies, and one extra-site study of a sequence taken from the slope beyond the sanctuary of Ribemont-sur-Ancre (Somme). Firstly, the results of these analyses highlight the methodological aspects, in order to show which contexts are favorable to pollen analyses, and which are less so. Secondly, when a few favorable contexts have been selected, a reliable picture of the landscape can be suggested, which at the same time favours an understanding of the impact these specific sites had on their environment. Traduction : Margaret & Jean-louis CADOUX.