This paper is an introduction to the concept of multiple fortifications, with an overview of Bronze and Iron Age fortifications in northern Central Europe and southern North Europe. Fortifications are understood as enclosures or delimitations marked with dikes, ditches, palisades, or similar constructions. The history of research into these fortifications is summarized, with a focus on chronology. The classification of fortified sites is also discussed. Lists of sites, radiocarbon dates, and a map of 403 fortifications are included in the text.