First High-resolution GPR and Magnetic Archaeological Prospection at the Viking Age Settlement of Birka in Sweden IMMO TRINKS 1,2 * , WOLFGANG NEUBAUER 2 AND ALOIS HINTERLEITNER 2,3 1 Swedish Central National Heritage Board, Archaeological Excavation Department, Stockholm, Sweden 2 Ludwig Boltzmann Institute for Archaeological Prospection and Virtual Archaeology, Vienna, Austria 3 Archeo Prospections, Central Institute for Meteorology and Geodynamics, Vienna, Austria ABSTRACT In May 2006 high-resolution measurements using ground-penetrating radar (GPR) and magnetic gradiometer systems conducted over selected areas at the site of the Viking Age settlement and trading place Birka in central Sweden demonstrated the suitability of these methods for archaeological prospection of Scandinavian proto-urban settlements. The non-invasive geophysical surveys revealed numerous structural details of the settlement: houses, property boundaries, track-ways, buried remains of the town ramparts dating from different building periods, including a gate, were mapped with a manually operated single-channel GPR system and a four-channel magnetometer array. The combination of these two prospection methods, state-of-the-art data processing and visualization and archaeological interpretation within a geographical information system resulted in valuable new information about the UNESCO World Cultural Heritage Site Birka-Hovgården. We present methodology and results of this first archaeological prospection case study conducted in 2006. Copyright © 2014 John Wiley & Sons, Ltd. Key words: Ground-penetrating radar; magnetic; interpretation; Scandinavian Iron Age; Viking settlement Introduction Since its set-up in April 2005 the archaeological prospection unit of the Archaeological Excavation Department (Arkeologiska UppdragsVerksamhet, UV in short), now the Contract Archaeology Service of the Swedish Central National Heritage Board, carried out a number of archaeological prospection trial sur- veys in Sweden, in order to gain experience and collect representative data samples with respect to different archaeological sites and geological environments, as well as to test the newly acquired geophysical mea- surement systems. During four days in May 2006 first ground-penetrating radar (GPR) and magnetometer test measurements were conducted at the site of the Iron Age trading place and settlement Birka on the island of Björkö in Lake Mälaren, some 30 km west of Sweden’s capital Stockholm. In this article we provide a brief description of the site, earlier archaeological prospection investigations conducted on Björkö, and subsequently present the fieldwork and results of the geophysical archaeological prospection test measure- ments of 2006. A detailed archaeological interpretation of the data is presented, as well as future perspectives and a conceptualization for further non-invasive inves- tigations of this unique world cultural heritage site. Site description Since 1993 the archaeological site of the Viking town and trading place Birka has been part of the UNESCO World Cultural Heritage Site Birka-Hovgården (ICOMOS, 1993). Hovgården, located on the neighbouring island of Adelsö, is being considered as the homestead of Birka’s rulers and Viking royalty (Nerman, 1918). It is generally assumed that Birka was founded in the first part of the 8th century AD (Magnus and Gustin, 2009) and that the town grew and existed for some 200 years until ca. AD 970, when it was abandoned * Correspondence to: Immo Trinks, Ludwig Boltzmann Institute for Archaeological Prospection and Virtual Archaeology, Hohe Warte 38, 1190 Vienna, Austria. E-mail: immo.trinks@archpro.lbg.ac.at Copyright © 2014 John Wiley & Sons, Ltd. Received 20 August 2013 Accepted 20 January 2014 Archaeological Prospection Archaeol. Prospect. 21, 185–199 (2014) Published online 4 March 2014 in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/arp.1481