Site in southern Zealand, Denmark, of a well-preserved Viking fortress of c 1000 AD. It is an insular type Viking military camp with a central circular fortification, substantial earth-and-timber bank, and four timber gates. The internal enclosure is divided into four quadrants each containing four boat-shaped longhouses. Trelleborg has a concentric outer defensive bank and an adjoining enclosure and 13 additional buildings between the two enceintes. Trelleborg was used between the mid-10th and early 11th centuries.