Dun (Archaeology)

A dun (from Scottish Gaelic dùn and Old Irish dún, derived from Proto-Celtic *dūnom, meaning "fort," "citadel," or "enclosed stronghold," cognate with Gaulish -dunum and Old English tūn) is a prehistoric and early historic drystone fortified enclosure, cliff-top citadel, or monumental thick-walled homestead constructed across the Atlantic façade of Scotland (especially Argyll, the Inner and Outer Hebrides, and Sutherland) and Ireland between approximately 600 cal BCE and 800 cal CE. Within British archaeology, the term encompasses both small, roofed circular or oval drystone Atlantic roundhouses (typically 10 to 20 meters in internal diameter with walls 3 to 5 meters thick) and larger irregular, topographical cliff-edge or rocky-knoll enclosures (dun enclosures and nuclear forts) whose stone ramparts follow the defensible contours of crags, stacks, and coastal headlands. Rather than representing an isolated architectural class, duns occupy a central position along the Atlantic Scottish and Irish settlement continuum alongside hollow-walled brochs, radial-piered wheelhouses, coastal promontory forts, pyrometamorphic vitrified forts, and artificial wetland crannogs.

Throughout the first half of the twentieth century, surveyors for the Royal Commission on the Ancient and Historical Monuments of Scotland (RCAHMS) divided drystone fortifications in Argyll and the Hebrides into three rigid size-and-plan tiers:

1. Forts (Hillforts): Enclosures exceeding ~0.15 hectares in internal area, typically defended by multiple ramparts enclosing numerous domestic timber or stone huts (see hillfort).
2. Brochs: Tall, strictly circular drystone towers characterized by hollow double-skinned walls (murus duplex), superposed intramural galleries tied together by flat stone lintels, a vertical voided window ladder, and a low rebated entrance passage with bar-holes and guard cells (see broch).
3. Duns: Small circular, oval, D-shaped, or irregular drystone structures (usually under 375 m² in internal area) capable of housing an extended family group or local aristocratic household, whose thick drystone walls enclosed a courtyard or supported a single conical timber roof.

Beginning in the 1980s, stratigraphic re-evaluations led by Dennis Harding, Ian Armit, and Euan MacKie demonstrated that the traditional distinction between a "broch" in northern/western Scotland and a "galleried dun" in Argyll was largely an artifact of regional antiquarian terminology and post-abandonment stone robbing. In his landmark synthesis of the Atlantic Roundhouse, Armit classified classic brochs, galleried duns, and solid-walled duns as functional variants within a single "Broch–Dun Architectural Continuum" spanning the Scottish Iron Age.

Excavations across Argyll, Skye, and the Western Isles reveal sophisticated drystone masonry techniques adapted to local metamorphic schists, Lewisian gneiss, Dalradian epidiorite, and Old Red Sandstone:

1. Solid-Walled Duns vs. Galleried Duns (Murus Duplex)

• Solid-Walled Duns: Constructed with a single thick wall (3.0 to 4.5 meters wide) composed of carefully coursed, battering outer and inner stone faces retaining a compacted core of rubble and turf. An internal stone scarcity ledge (scarcement) projecting 0.2 to 0.4 meters from the inner wall face at a height of 1.5 to 2.2 meters supported either a raised wooden ring-beam floor or the rafters of a heavy thatched roof, while intramural stone staircases ascended within the thickness of the wall to a parapet walk.
• Galleried Duns: Recorded across Kintyre, Lorn, Skye, and Barra (such as Kildonan and Dun Grugaig), galleried duns feature hollow double-skinned walls (murus duplex) separated above ground level by narrow intramural galleries spanned by horizontal tie-slabs, closely matching the structural engineering of Hebridean brochs even when the overall ground plan is oval or D-shaped to fit an irregular rocky outcrop.

2. Entrance Architecture and Timber-Laced Vitrification

Entry into a dun was tightly controlled through a single narrow, lintelled passage (typically 0.9 to 1.3 meters wide and 3 to 5 meters long) equipped with projected stone door-checks (rebates) against which a heavy oak plank door closed, backed by opposed drawbar sockets (allowing a stout wooden beam to be slid across the passage from a deep channel in the wall) and intramural guard cells or dog-leg bends. In several Scottish duns—such as Rahoy in Morvern, excavated by V. Gordon Childe in 1936–1937, and Dun Skeig in Kintyre—the drystone wall core was reinforced with transverse oak tie-beams (murus gallicus-like timber lacing). When destroyed by high-temperature conflagrations exceeding 1,050–1,150 °C, the biotite- and feldspar-rich rubble melted into dark vesicular silicate slag, turning the monument into a small vitrified fort.

AMS radiocarbon dating (¹⁴C) and ceramic/metallurgical typo-chronologies across Argyll and the Hebrides demonstrate a multi-phase occupational biography spanning over a millennium:

1. Early and Middle Iron Age Construction (c. 600 BCE–200 CE)

The earliest drystone duns and small cliff-top enclosures emerged during the Late Bronze Age to Early Iron Age transition (as at Rahoy, yielding both a socketed bronze axe and an early iron blade) and proliferated across the last four centuries BCE. During the Roman Iron Age (1st–2nd centuries CE), duns in Argyll and southern Scotland yielded Roman terra sigillata (Samian ware), melon beads, and bronze fibulae acquired through diplomatic gift exchange or coastal trade across the Antonine Wall frontier.

2. Early Medieval Reuse and Nuclear Forts in Dál Riata (c. 400–850 CE)

Unlike northern Scottish brochs—many of which collapsed or converted into cellular wheelhouses by the 3rd century CE—numerous duns in Argyll (the heartland of the Gaelic kingdom of Dál Riata) remained elite residences or were systematically refurbished between the 5th and 9th centuries CE:

• Kildonan Bay (Kintyre): Excavated by Horace Fairhurst (1936–1938), this galleried dun preserved three primary structural phases extending from the 1st–2nd centuries CE through the 6th–9th centuries CE, yielding rotary querns, iron slag from on-site bloomery smithing, glass beads, and a copper-alloy penannular brooch.
• Nuclear Forts and Royal Citadels (Dunadd, Dunollie, Dundurn): Proposed as an architectural model by Robert B. K. Stevenson (1949) and refined by Leslie Alcock and Alan Lane, early medieval kings in Dál Riata and Pictland incorporated an apical summit dun into a tiered hierarchy of lower stone-walled courtyards looping down a craggy rock boss. At Dunadd in the Moine Mhòr bog of Kilmartin Glen (excavated by Alan Lane and Ewan Campbell in 1980–1981), the summit dun looked down over lower enclosures where royal goldsmiths cast high-status Hunterston-type penannular brooches in two-piece clay molds while importing Continental E-ware pottery, Bordeaux wine, and Germanic glass vessels, alongside the bedrock inauguration stone carved with a life-sized human footprint, an incised Pictish boar, and an Ogham inscription.

In Irish archaeology, the cognate term dún (alongside caiseal / cashel and cathair / caher) designates both monumental coastal promontory and cliff-edge citadels and early medieval drystone ringforts:

• Dún Aonghasa (Inishmore, Aran Islands, Co. Galway): Perched at the edge of a sheer 87-meter vertical limestone sea cliff facing the Atlantic Ocean, Dún Aonghasa (excavated by Claire Cotter during the Discovery Programme in 1992–1995) began around 1100–800 cal BCE as a Late Bronze Age settlement with bronze-casting workshops producing swords, spearheads, and sunflower pins. During the Iron Age and early medieval period (~500–800 CE), builders reconstructed the inner semicircular citadel with terraced drystone walls 5.8 meters thick and 4.9 meters high, surrounded by three outer stone ramparts and a dense defensive band of upright jagged limestone pillars (chevaux-de-frise, up to 1.75 m tall) designed to impede mounted or charging attackers.
• Grianán of Aileach (Co. Donegal) and Staigue Fort (Co. Kerry): Circular drystone cashels with triple-terraced internal wall-walks and X-patterned intramural staircases that served as regional royal strongholds of the northern Uí Néill and Munster dynasties.

What is the difference between a broch and a dun?

A broch is always strictly circular in ground plan and was built as a tall, multi-story hollow-walled drystone tower (up to 10–13 meters high) with superimposed intramural galleries and a vertical stack of voided lintelled openings. A dun exhibits a wider range of ground plans (circular, oval, D-shaped, or irregular following a rocky crag) and generally stood lower (a single story or lofted roof), with either solid drystone walls or a single basal gallery—though archaeologists view brochs and galleried duns as overlapping expressions of the broader Atlantic roundhouse tradition.

Why are some Scottish duns vitrified?

Several duns—such as Rahoy in Morvern and Dun Skeig in Kintyre—had internal horizontal and transverse oak beams built into their drystone rubble cores for structural reinforcement. When these timber-laced walls were set ablaze during warfare or ritual decommissioning, internal temperatures reached 1,050 °C to 1,200 °C, partially melting the stone core into glassy vesicular slag just like larger vitrified forts.

Who lived in duns during the Scottish Iron Age and Early Middle Ages?

Most small roofed duns (10–20 meters across) housed an extended affluent farming household or local landholding lineage who controlled surrounding arable pastures, cattle herds, and coastal sea-lanes. Larger multi-terraced crag-top duns such as Dunadd and Dunollie served as the fortified royal capitals and metallurgical patronage centers of early medieval Gaelic kings in Dál Riata.

1. Armit, I. (2003). Towers in the North: The Brochs of Scotland. Tempus Publishing. https://doi.org/10.1017/S0003598X00093133
2. Harding, D. W. (1984). "The function and classification of brochs and duns." In R. Miket & C. Burgess (Eds.), Between and Beyond the Walls: Essays on the Prehistory and History of North Britain in Honour of George Jobey (pp. 206–220). John Donald Publishers. https://doi.org/10.9750/PSAS.114.206.220
3. Lane, A., & Campbell, E. (2000). Dunadd: An Early Dalriadic Capital. Oxbow Books. https://doi.org/10.2307/j.ctvh1dwp2
4. Fairhurst, H. (1939). "The galleriedf dun at Kildonan Bay, Kintyre." Proceedings of the Society of Antiquaries of Scotland, 73, 185–228. https://doi.org/10.9750/PSAS.073.185.228
5. Cotter, C. (2012). The Western Stone Forts Project: Excavations at Dún Aonghasa and Dún Eoghanachta (2 vols.). Wordwell / The Discovery Programme. https://wordwellbooks.com/index.php?route=product/product&product_id=1432