A Martin Down enclosure is a small, usually sub-rectangular area bounded on all sides by an earthwork comprising a ditch and internal bank and/or fence. Sites in this class tend to be small, generally encompassing areas of less than 0.3ha, the boundaries of which are marked either by single ditches and internal banks or by consolidated lynchets. They are generally found on the lower margins of hillsides and in valley bottom locations, where they have been recognised, either as cropmarks or (rarely) as low earthworks. Whilst many sites in this class possess ditches and banks on all sides, certain examples appear to have been open on one or even two sides.
It is important to differentiate between Martin Down enclosures and those rectilinear defended sites of a similar scale which were constructed and used during the later Iron Age (see separate class description).
Sites in this class date to the Later Bronze Age and are generally assumed to be associated with animal husbandry and/or settlement, an interpretation supported by a common association with field systems. Although sites in this class appear to share a number of functional characteristics with contemporary enclosures (eg. Springfield type enclosures), distinctions can be drawn upon the basis of their morphology.