The recent re-analysis of the earlier excavations at Aggersborg has highlighted some disturbing gaps in our knowledge of the site. It was judged that some of these problems could be solved by geophysical investigation. Aggersborg was considered to be a highly promising target for geophysical investigations for three reasons: first, the site formation – cut features filled with organic fill in chalk and chalk-rich glacial till or drift sand – was likely to give good contrast for magnetometry and GPR; second, the earlier excavations outline a clear interpretational frame for the survey, while leaving 80% of the site untouched; third, the earlier excavations also provide essential research questions, which could be investigated by the prospection.
The general aims of the survey were to clarify the spatial structure of the archaeological site and to identify any further traces of structures pertaining to the fortress and settlement, including cut features, hearths and stone paving, as well as, potentially, levelling layers, cultural layers, areas with potential for waterlogged preservation, or possible evidence of a conflagration. The key question, however, concerned the concentration and extent of SFBs. Excavations in the eastern part of the site showed a dense concentration of these, while another cluster may be indicated by test trenches further to the west. Some field notes suggested that the fortress area might have had levelling layers, which were only recognised as such in a late phase of the excavations. In that case, it was possible that the concentration of SFBs continued under these layers into the apparently empty areas.