Between the 8th and 12th century, the Polabian Slavs built numerous strongholds in what is now north-eastern Germany (Mecklenburg-Vorpommern, Brandenburg, eastern Holstein). These characteristic fortifications, with ramparts in a wood-earth construction and defensive ditches, occupied favourable positions for defence and always showed signs of settlement use. Over time, they changed their appearance and had various military and political, and sometimes economic and religious, functions. Archaeological excavations and written sources provide information about this. Reliable dating, based in particular on dendrochronology, allows a substantial interpretation of the development of Slavic strongholds and the purpose of fortifications against the background of social and military development. The lecture provides an overview of the Polabian strongholds and summarises the current state of research.