A cursus is an elongated rectilinear earthwork enclosure whose length is over 250m and whose long axis is more than ten times the short axis. The sides are usually defined by a bank and external ditch, but occasionally by a line of closely-set pits. The two long sides run roughly parallel, and may incorporate earlier monuments such as long barrows. The function of cursuses is not known, although they are presumed to be ritual/ceremonial monuments.
The name was coined by the 18th century antiquary William Stukely for the example at Stonehenge, which he thought was intended for the celebration of funeral games and compared, quite misleadingly, to a Roman racetrack. The Stonehenge cursus measures some 2750 to 100m, but the longest known cursus, in Dorset, runs for nearly 10km. This class of monument is found only in Britain, and belongs to the later part of the Neolithic. Some examples incorporate or are aligned on earthen long barrows, and at Thornborough in Yorkshire a cursus underlay a henge.
Long mortuary enclosures are are sometimes confused with cursuses, but these tend to be much shorter, generally less than 150m long whereas cursuses are typically over 250m long. The two possible cursuses in Buckinghamshire may be long mortuary enclosures, at Southend Hill in Cheddington and at Ivinghoe Beacon.
The majority lie on the flat well-drained gravel terraces of major river valleys, but this may be because aerial photography is the main source of new discoveries. Larger cursuses tend to cut across the natural grain of the countryside, whereas shorter cursuses are often set out on a single gently sloping block of land. Cursuses on higher ground tend to run along the spring-line, while those on lower ground frequently lie at right-angles to a river or stream. Some cursuses run between two rivers, and at Stanwell, Surrey, the cursus appears to cross two rivers.