When Trelleborg was excavated in the 1930s as the first of the great ring fortresses of the Viking Age, it was a true archaeological enigma. Why was it built, and by whom? Today we know that the strange, circular rampart at Slagelse was built under King Harald Bluetooth in the late 900s. Trelleborg, now a UNESCO World Heritage Site, has helped reshape our image of the Viking Age in Denmark. The book follows the work of the archaeologists from the first careful excavations and speculations to the sensational discoveries that have led to what we know today about Trelleborg. Viking-Age Ring Fortresses tells the fascinating story of five of the most important monuments of the Vikings in Denmark: Trelleborg, Aggersborg, Fyrkat, Nonnebakken and Borgring. The series is a story of our knowledge about the Viking Age, and at the same time it focuses on the questions and riddles that the fortresses still hold.