The Discovery Programme has recently initiated a programme of geophysical investigations as part of the Late Iron Age and Roman Ireland (LIARI) Project. The project seeks, amongst other things, to shed light on settlement and society in Ireland during the first five centuries AD, and will involve a critical reappraisal of the nature and impact of interaction with the Roman world. Geophysical survey is one of a range of non-invasive technologies being utilised to identify and investigate some of the landscapes and sites used during this enigmatic period in late prehistory. Various prospection techniques, including those that measure changes in the magnetic properties of the soil (magnetic gradiometry) and variations in ground moisture (electrical resistance) are being employed to investigate a variety of sites whose potential to reveal insights into the late Iron Age has been highlighted by previous research. These techniques are widely used in modern investigations due to their ability to detect a broad range of sub-surface archaeological remains, including ditches and pits, stone buildings and industrial features associated with metalworking and pottery production.

Geophysical survey is currently underway at a number of different sites in County Dublin, with further investigations planned elsewhere in the country during the coming months. Although still at an early stage, the surveys have already revealed a variety of previously unrecorded archaeological sites and features (see below), and it is anticipated that future work will continue to yield new and exciting discoveries.

The image shows the results of a recent gradiometer survey undertaken as part of the LIARI Project. In addition to a host of other features of varying shape and size – some of which may represent ancient field boundaries – at least four circular 'ring-ditches' were revealed by the survey. While the exact function and date of these circular features cannot be established on the basis of geophysics alone, they may comprise the remains of prehistoric funerary monuments. One of the more interesting is a 'double ring-ditch' measuring about 10m in overall diameter, which is suggestive of a type of burial monument known to have been in use during the first millennium BC.