While geophysical prospection for iron ores has a long history in Sweden the use of geophysical archaeological prospection has been limited compared to other countries. In this paper we discuss the likely reasons for this situation and present a brief history of geophysical prospection and in particular geophysical archaeological prospection in Sweden. The first use of different prospection methods, such as metal detection, earth resistance, magnetic, ground-penetrating radar, seismic and electro-magnetic prospection in Swedish archaeology are presented. The archaeological Iron Age sites of Uppåkra and Birka have been subject to relatively intensive prospection activity and are therefore mentioned separately. An overview of the current situation of geophysical archaeological prospection and related issues is given, and pitfalls and possibilities are discussed. The paper finishes with an outlook on possible future developments.

The project Arctic Sweden initiated during the International Polar Year (2007-2008) was aimed at investigating aspects of the natural and cultural environment in this area. During the summer of 2008 archaeological excavations and geophysical prospection surveys were carried out in the mountain tundra region of north-western Sweden. The investigations focused on locating settlement remains connected with a Middle Neolithic tool production site discovered by archaeologists in 2001. Magnetic susceptibility surveys using the MS2D system by Bartington Instruments and an EM38 by Geonics measuring the Inphase component of the electromagnetic field were used for the prospection of measureable traces of anthropogenic activity and structures such as hearths and middens within the estimated settlement area. Soil samples for phosphate analysis were also collected and analysed using a field analysis method developed by Merck. The magnetic susceptibility measurements successfully located a waste heap containing fire-cracked stones and refuse from a seasonal settlement. The results of the survey were confirmed by subsequent archaeological excavations, which also revealed a piece of resin with the imprint of a human tooth. One additional piece of resin dated the site to 3340 to 3100 BC. The soil phosphate analysis showed slightly increased values over the central part of the site and over the heap of fire-cracked stones, suggesting the applicability of the method to a mountain tundra environment. Comparison between the MS2D and EM38 measurements revealed a weak impact of the bedrock on the results, indicating a potential for the applicability of magnetic surveys to this specific type of environment. Future geophysical archaeological prospection in the Swedish mountain tundra region could benefit from a combined approach using high-resolution magnetometry and magnetic susceptibility measurements.

Archaeological investigations and clear aerial photographs have identified the presence of house foundations within several ring forts on the island of Öland, situated east of the Swedish mainland. One of them, Sandbyborg, was selected for further investigations by means of a ground-penetrating radar (GRP) and magnetometry survey. The purpose of the geophysical survey was to establish the fort’s spatial layout, to identify any internal constructions within the houses and to investigate whether the fort had multiple building phases. Targeted archaeological excavations was subsequently carried out to verify the validity of the geophysical results and to recover datable material that would enable the understanding of how Sandbyborg was chronologically related to the other ringforts of the island. This information could then be used to better understand the function of Sandbyborg. The results of the geophysical survey clearly show the presence of 36 or 37 stone foundations for houses situated radially aroundthe wall of the fort as well as 16 or 17 similar house foundations in a central building group. The geophysical results also provided information on the possible location of hearths, kilns and pits within the fort and also confirm the location of a third gate situated in the north-western part of the fort. The spatial layout and inner size of Sandbyborg is very similar to one of the other Migration Period ring forts on Öland, Eketorp II. However, there is no evidence of multiple building phases in the data from Sandbyborg. The subsequent excavations showed a very good correlation with the geophysical data. Datable finds, a ¹⁴C date from a human metatarsal found in one of the trenches and the lack of geophysical evidence of multiple building phases indicate that the ringfort was used for a limited period of time during thelate fourth century AD. Given the available evidence it is suggested that Sandbyborg primarily was used for military purposes or as a place of refuge intimes of unrest as its location in the outfields, far from arable lands, contradicts an interpretation of Sandbyborg as a fortified village, but as the evidence about the ringforts on Öland is restricted a continued use of geophysical prospection and excavations within the other forts is suggested as a means of obtaining a deeper understanding of the purpose and context of these highly interesting structures.

Gradiometer surveys have been carried at three Iron Age and early medieval sites on the island of Gotland, Sweden. Previous experiences of poorly executed magnetic surveys combined with a misconception among archaeologists that the Gotlandic sedimentary bedrock would preclude the success of any magnetic investigations on the island have, until now, prevented the extended use of the method within archaeological projects. The purpose of the present study was to test this presumption while searching for in situ buried remains of high-temperature crafts, such as metal and glass working. The location of the survey grids was guided by concentrations of previously recovered hightemperature craft finds from metal detector surveys and excavations. The results indicate that the magnetometer is a valuable tool for detecting the presence of preserved high-temperature craft structures in the Gotlandic soil. An additional result indicates that in this area the magnetometer can easily identify remains of ploughed-over Iron Age stone foundation houses and stone boundary walls. This is possible because of the prehistoric population’s preference of using glacially deposited, igneous rocks in such constructions. It can thus be concluded that the uniformly nonmagnetic character of the Gotlandic bedrock provides excellent conditions for conducting magnetic surveys.

A ground-penetrating radar (GPR) survey and an archaeological excavation of the buried remains of the Medieval Dominican convent in Sigtuna (Raä 30) produced new information on the ground plan of the convent and the condition of the buried structures remaining at the site. The site has hitherto seen surprisingly little archaeological investigations, and it is now over 30 years since the previous fieldwork. In addition to the foundation walls of the convent and adjoining structures, GPR also revealed an earlier building phase and a previously unknown lavatorium connected to the southern range. These interpretations were confirmed by excavations in September 2009. A suggestion as to the function of the various buildings, based on comparison with other convents, is offered.