This paper discusses the landscape pattern made by the reaves—second millennium bc land boundaries—of South Dartmoor. The upper moorland of the South Moor was probably used as common grazing by 6–7 major sociopolitical units. Each possessed its own grazing land, normally in a valley zone near settlement enclosures. Each group had a ‘parallel system’ of reaves used partly for cultivation. 2 or 3 groups shared the Hameldon Ridge, in similar fashion. The paper discusses gateways, gang junctions, alterations to reaves, and the question of their original height, concluding that stock was probably watched, so that reaves were primarily boundaries, although some may have been built as barriers. The contour reaves, which separate the common grazing land from that in the valley zones, seem to have been less important, and perhaps built later, than the reaves between the sociopolitical groups, and the contour reave zone seems to have been chosen quite often by the builders of stone rows. There were subdivisions within the private grazing areas. It is concluded that the pattern of several territorial groups, clustered round an extensive, probably common resource, is well-known in second millennium British prehistory, and deserves further study.