Hilltop enclosures are substantial areas of ground, usually situated on the top of a hill or a plateau, surrounded by univallate earthworks of relatively slight proportions. Not all hilltop enclosures are entirely surrounded by a boundary, but can be open along one side. While this may be an original feature of inland sites, on examples located along cliff edges the boundaries closest to the coast could have been lost to erosion. The internal area of the majority of hilltop enclosures measures between 10ha and 40ha, although much larger examples up to and exceeding 100ha are included in this description. The ground plan of this class of monument is generally irregular, while the area enclosed tends to be sub-rectangular or elongated in shape. Some of the enclosures may be sub-divided by cross-banks.
The main components of hilltop enclosures are the earthworks; the entrances; and internal features. The majority of earthworks consist of a bank separated from an external ditch by a berm, and occasionally include a counterscarp bank. Entrances usually number between two and three and comprise simple gaps, although short passages created by inturning the ends of the ramparts are recorded on some sites. Excavations within hilltop enclosures have revealed large "empty areas", and/or a series of sparsely scattered features, which include postholes, stakeholes, hearths, and a small number of pits. Reconstructed buildings are often square/rectangular in shape and are defined by four to six postholes, which are generally thought to have supported raised granaries. The number of artefacts is, in most reports, described as "low".
Hilltop enclosures are usually interpreted as stock enclosures or as sites where agricultural produce was stored.
Care should be taken to distinguish hilltop enclosures from sites exceeding 10ha which are more strongly defended, by the location of boundary earthworks above steep scarps; by more massive ramparts; and by partial or complete multivallation. Although these may have begun as relatively slight enclosures (a fact only confirmed by excavation) in their final form they appear to have occupied a rather different role within the contemporary settlement pattern. Ham Hill, for example, has produced a much wider range of artefacts than occur on hilltop enclosures, including iron currency bars, late Iron Age coins and continental imports, while its use appears to have extended into the Romano British period.
Further confusion may arise when attempting to distinguish between hilltop enclosures and oppida. This can usually be resolved by a consideration of the topographic setting. Unlike hilltop enclosures, oppida are often located on low ground adjacent to river systems. Suggested examples, which re-use earlier hillforts, such as Bigbury in Kent, are surrounded by much larger earthworks than occur on hilltop enclosures.
Also excluded from this description are promontory sites which are defined by short lengths of earthwork which are located across one or more narrow spurs.