The majority of enclosed sites in Argyll comprise structures classified as forts and duns with only 26 classified as enclosures and 6 sites categorised as brochs. The latter grouping is concentrated in the north and west of the area and, including a southerly example on Arran, are all located on the Argyll islands (Figure 90).
Defensive structures in the west of Scotland, particularly Argyll, are often known as dùns, a Gaelic vernacular term that can be used to classify any fortified place, or even a naturally defensive place. The term ‘dun’ was adopted by RCAHMS and is now used to classify smaller (up to 375m²) thick walled stone enclosures dating from around 500 BC to the early historic period. Forts by inference are larger in size and could date to an earlier period than duns. As a classification, these at the time necessary groupings, now seem unsatisfactory as duns and forts (and brochs) form a heterogeneous group, varying in size with different structural morphologies and landscape locations. The function, date and social significance of these structures across Scotland have been much discussed, particularly that of the Atlantic Roundhouse, although this has tended to focus on the broch (and to a lesser degree the wheelhouse) conducted, with a few exceptions, within a decidedly insular framework (Neike 1990; Hingley 1992; Harding 1997, 2004a, Armit; 1991, 2004 Gilmour; 2000, 2005, Parker Pearson et al.; 1996, 1999, Henderson; 2000, 2007 MacKie; 2000, 2007, 2008, 2010). Similarly the chronology and typology of enclosed Iron Age sites in Argyll has been open to debate particularly that between Nieke/Alcock and Harding (Neike 1990; Alcock 2003, Harding; 1997, 2004a).
Henderson and Gilmour have recently summed up the debate and argued that most of the excavated circular sites date to the second half of the 1st millenium BC and while many dun sites have produced artefacts of later date, they also have evidence of earlier but poorly dated occupation or constructional phases such as at Druim an Duin (NMRS No. NR79SE 1) and Ardifuir (NMRS No. NR79NE 2). They argue that few of the excavated sites have reliable 1st millennium AD dates for their construction (Henderson and Gilmour 2011). One of the major factors that influence this debate is the paucity of diagnostic finds from many excavated sites or the absence of securely provenance and dated finds where they are more abundant. The dates attributed to some artefacts, particularly from earlier excavations have also been questioned and are in need of systematic reassessment. With this caveat in mind and until this work is done we still in many cases have to rely on the dates given by the original publications or site reports. All excavation work at these type sites has however added something to the overall picture of Iron Age settlement in Argyll and the following summaries use the original RCAHMS typology of sites for ease of reference.