In 1988-1989, a campaign of eight months of rescue excavations prior to the construction of a parking took place on the Grand' Place, presently the place Charles de Gaulle, in Lille. They documented eight identifiable phases, ranging from the 13th to the 15th century and reflecting of the development of this public square, which had previously long been subject to flooding by the nearby river Deule. Until the 13th century, the area was not used permanently, though it yielded traces of a few presumably temporary structures and remains related to circulation (horse-shoes). Afterwards, intermittent raising and levelling operations reflect continuing efforts to make the area usable, while from the 14th century onwards recurrent but often somewhat chaotic patterns of temporary structures - presumably temporary market stalls - occur until the square is paved (15th century). The operation provided the occasion to confront the archaeological evidence with the historical information and to assess the meaning of the former in relation to the broader historical context, particularly in relation to the topographical development of the town. The relation between the square and the forum" of Lille is equally tested and found to be wanting, while the excavations also provided indications related to the continuing struggle again flooding and the canalisation of the Defile. The present contribution also includes a number of thoughts concerning the importance of the archaeological study of public squares, their significance in historical terms, the methodology involved and the meaning of the evidence for a better understanding of the urban texture and street pattern as a whole. A brief comparison with a few other cases ('s-Hertogenbosch, Ghent) suggest the Lille Grand' Place to conform fairly well to a broader pattern, but more documentation is needed. A number of preliminary reflections pay attention to the problems concerning the terminology, identification, characterization, functions and archaeological study of urban open spaces and public squares.