Hillslope Enclosure

A hillslope enclosure (also classified in regional British typologies as a hill-slope fort, slope enclosure, or multiple-enclosure fort) is a Late Bronze Age, Iron Age, and Romano-British banked-and-ditched settlement earthwork constructed across southwestern England (Devon, Somerset, and Cornwall), Wales, and the Welsh Marches primarily between 600 BCE and 200 CE. Unlike a classical summit hillfort—which occupies the highest, most defensible contour of an isolated hilltop—a hillslope enclosure is deliberately sited on a sloping valley side, mid-slope terrace, or gently inclined ridge spur (typically enclosing 0.4 to 3.5 hectares), where rising ground upslope overlooks the interior of the monument. Initially dismissed by 19th-century military antiquarians as tactically inept fortifications, modern landscape archaeology, geophysical surveys, and open-area excavations pioneered by Aileen Fox, Geoffrey Wainwright, Henrietta Quinnell, and Toby Driver have demonstrated that hillslope enclosures were engineered not as military citadels against siege warfare, but as sheltered, water-accessible, socially prestigious mixed pastoral-arable homesteads and stock corrals.

Why did Iron Age builders in Devon, Exmoor, Somerset, and Wales expend thousands of labor-hours digging V-shaped rock ditches and raising earthen ramparts 2 to 4 meters high on a valley slope that could be looked directly down into from the higher ridge crest only 100 meters upslope? Spatial GIS analysis and paleoenvironmental modeling identify four agronomic and social imperatives behind hillslope siting:

1. Microclimatic Shelter from Atlantic Gales: Across upland southwestern Britain and west Wales (between 150 and 350 meters above sea level), exposed hill summits experience salt-laden prevailing southwesterly gales, driving rain, and winter frost. Siting the settlement 30 to 80 meters downslope on a south-, southeast-, or east-facing valley flank reduced wind velocities by 40% to 60% and maximized winter solar insolation for circular timber Atlantic roundhouses and outwintered livestock.
2. Perennial Spring-Line and Stream Access: Summit hillforts on porous limestone, sandstone, or slate ridges lacked internal water sources, requiring inhabitants to haul water up steep slopes from valley rivers. By positioning hillslope enclosures along the geological spring-line or directly above a perennial valley brook, builders secured year-round water for large herds of cattle (Bos taurus) and horses within a short walk of the compound.
3. Ecotonal Position Between Arable Valley Loams and Upland Pasture: Hillslope enclosures occupy the ecological boundary (ecotone) between deep, well-drained colluvial brown-earth soils on the lower valley slopes—cultivated as coaxial Celtic fields for spelt wheat, emmer, and barley—and the open heather-and-grass moorland ridges upslope used for summer transhumance grazing.
4. Cross-Valley Visual Theatricality: Because a sloping enclosure tilts toward the valley floor, its concentric ramparts and interior roundhouse roofs were angled like a stage toward travelers moving along the valley river corridor and toward neighboring communities living on the opposite side of the valley.

In her foundational 1952 study Hill-Slope Forts and Related Earthworks in South-West England and South Wales, Lady Aileen Fox divided hillslope enclosures into two primary architectural traditions that coexisted within the same river valleys:

• Simple Univallate Hillslope Enclosures: The most numerous class across Devon, West Somerset (Exmoor and the Quantock Hills), Pembrokeshire, and Carmarthenshire consists of a single circular, oval, or sub-rectangular bank and external ditch (univallate) enclosing 0.3 to 1.5 hectares on a valley side. In Cornwall and western Devon, smaller domestic hillslope enclosures grade continuously into the Late Iron Age and Romano-British farmstead tradition known locally as rounds (Cornish ker). At Walesland Rath in Pembrokeshire—stripped and excavated by Geoffrey Wainwright in 1967–1968—an oval univallate bank (65 × 50 meters internally) on a valley slope enclosed a ring of circular timber roundhouses alongside continuous timber-framed lean-to ranges built against the inner tail of the rampart, dated by radiocarbon dating to c. 300 cal BCE–100 CE.
• Widely Spaced Multivallate ("Multiple-Enclosure") Forts: A regional specialty of Devon, Cornwall, and South Wales (exemplified by Milber Down, Clovelly Dykes, Denbury, Wooston Castle, and Bury Castle in Devon; Tregeare Rounds and Warbstow Bury in Cornwall; and Y Gaer Fawr and Harding's Down in Wales) is the multiple-enclosure hillslope fort. Unlike a Wessex multivallate hillfort (where two or three ramparts are packed closely together to maximize sling-defense depth), a southwestern multiple-enclosure site surrounds a small inner domestic compound (0.3–0.6 ha) with two, three, or four widely spaced concentric ramparts separated by broad, flat inter-vallum belts (15 to 45 meters wide) or asymmetric lobe-shaped annexes. As Fox demonstrated through comparisons with contemporary banjo enclosures in Wessex, the central inner enclosure housed the resident extended family's timber roundhouses and four-post granaries, while the wide outer concentric belts served as predator-proof night corrals and winter fodder yards accessed via a sunken droveway (holloway).

Excavations at Milber Down (Devon), Collfryn (Powys), Mynydd Bychan (Glamorgan), and Berry Ball (Devon) paired with archaeobotany and zooarchaeology illuminate the material life of hillslope enclosure communities during the Middle and Late Iron Age (c. 350 BCE–75 CE):

1. South-Western Decorated ("Glastonbury") Ware: Across Somerset, Devon, and Cornwall, hillslope enclosures yield burnished, curvilinear-incised South-Western Decorated Ware (decorated with La Tène compass-drawn scrolls and cross-hatched basketry panels), petrologically sourced by David Peacock to specialized gabbroic, granitic, and sandstone clay production centers.
2. Metallurgy and Prestige Bronzes: At Collfryn in the Welsh Marches, Bill Britnell's excavation of a triple-ditched hillslope enclosure uncovered bronze-casting crucibles, iron-smelting slag, four-post granaries, and a waterlogged defensive ditch preserving wooden structural carpentry. At Milber Down near Torquay, the inner ditch of the four-ring hillslope camp yielded three Late Iron Age / early Roman cast-bronze zoomorphic figurines—a duck carrying a round cake in its bill, a stag, and a bird with detachable wings—deposited as a ritual closure offering in the mid-1st century CE.

Whereas major martial summit hillforts in southern Britain were frequently slighted or abandoned during the Roman conquest of 43–78 CE, many hillslope enclosures (such as Walesland Rath, Collfryn, and Trevinnick) continued in uninterrupted agricultural occupation through the 1st to 3rd centuries CE, acquiring Roman Samian ware (terra sigillata), glass vessels, and iron agricultural tools before being superseded by medieval dispersed farmsteads and strip lynchet fields.

1. Fox, A. (1952). "Hill-slope forts and related earthworks in South-West England and South Wales." The Archaeological Journal, 109(1), 1–22. https://doi.org/10.1080/00665983.1952.10854047
2. Wainwright, G. J. (1971). "The excavation of a fortified settlement at Walesland Rath, Pembrokeshire." Britannia, 2, 48–108. https://doi.org/10.2307/525802
3. Britnell, W. (1989). "The Collfryn hillslope enclosure, Llansantffraid Deuddwr, Powys: Excavations 1980–1982." Proceedings of the Prehistoric Society, 55, 89–134. https://doi.org/10.1017/S0079497X00005351
4. Driver, T. (2013). Architecture, Regional Identity and Power in the Iron Age Landscapes of Mid Wales: The Hillforts of North Ceredigion. British Archaeological Reports (BAR) British Series 583. Archaeopress. https://doi.org/10.30861/9781407311234