Dartmoor, a granite massif in SW England, boasts the most completely preserved landscape of the 2nd millenium B.C. in Europe, with numerous burial cairns, houses, enclosures, fields, and territorial boundaries surviving. Systematic mapping of these remains has been in progress in the last decade, mainly by the University of Sheffield. This paper describes a low-lying area of moorland partially threatened by tungsten mining. The prehistoric fields on Crownhill Down represent a piecemeal layout in contrast to the systemic "reave" systems known elsewhere on the moor. Abandoned ca. 1000 B.C., the area was not recolonized for farming until the medieval period ca. 1000 A.C. in the period of land hunger that continued to the 14th century. Ditched field systems and boundaries and a longhouse (a farmhouse with accomodation for both humans and livestock) belong to this period. From the 16th century the Down has been mined for tin, arsenic, and tungsten. This present survey attempts to demonstrate the level of recording required to phase field systems.