An enclosed Oppida is a nucleated settlement of the Later Iron Age, covering an area in excess of 10ha, whose boundaries are marked by large earthworks comprising bank and outer ditch, which are generally taken to be of a defensive nature. They occur in three principal locations, on earlier, redefended hill-tops, on the sides of valleys, and immediately adjacent to rivers in southern, central and eastern England. These characteristic locations make it possible to differentiate between this class and the majority of hillforts.
Sites in this class share a number of characterisitics with "Unenclosed Oppida" (Cunliffe 1978), although these are excluded from this description since, as their title suggests, they lack any recognisable defences (eg. Prae Wood). It is also important to draw a distinction between these sites and "Territorial Oppida" - the extensive earthwork complexes within which a number of Enclosed Oppida are set (see separate class description).
Enclosed Oppida contain evidence for a variety of activities, suggesting that they may have been the centres within which a range of economic, political and religious services were concentrated. Many examples contain evidence for the development of zones within which particular activities (eg. productive or ritual) appear to have been emphasised.