Two examples of magnetic investigations of large barrows in Denmark and Crimea (Ukraine) are presented. The magnetic field over the Danish barrows containing megalithic graves results from the superposition of many different dipole anomalies from granite boulders. The magnetic map revealed a corridor and a chamber of a barrow in Draaby, which are adjacent to a similar, previously excavated feature. A circular wall of smaller stones, which surrounds the two chambers and corridors, is clearly visible on the magnetic map. The limestone building material used for the internal construction of the Scythian barrows in Crimea is practically nonmagnetic, while the soil in these regions has a significant magnetic susceptibility (about 10-100ϫ10 -5 ISO). This makes it possible to identify stone structures by their negative anomalies on magnetic maps. Each of the three large barrows is surrounded by a circular negative anomaly that is 50 m in diameter. The anomaly is caused by walls (cromlechs) inside the barrows. Within each barrow, a long negative anomaly (up to -20 nT) that starts at the cromlech and leads toward the center of the barrow is an indication of a rectangular stone construction inside the barrow (side crypt). The central part of each barrow is characterized by a positive or a negative anomaly, which reflects the state of preservation of the central chamber.

In Denmark iron production, by means of reducing bog-iron ore with charcoal, was carried out at least between the second and seventh century AD. Since the 1960s magnetic mapping of iron slag remains have been used extensively at several sites in the southwestern part of Jutland in Denmark (e.g. at Drengsted, Snorup, Krarup and Yderik). A description of some of the magnetic surveying results, ideas of magnetic modelling, and magnetic and chemical analysis of slag from some of these areas are given. The Danish Iron Age slag pits are strongly magnetic, and consequently they are quite easy to locate magnetically. The slag, however, is often magnetically non-homogeneous, and accordingly the remanent magnetic direction of the original magnetization is not uniform. Hence individual slag pits are not good recorders of the direction of Earth's magnetic field. Therefore dating of individual slag pits by means of a magnetic mastercurve, using either inversion and modelling of the magnetic field anomaly from the slag, or by using conventional palaeomagnetic techniques by orientated cores, are still difficult to make with sufficient resolution.

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