They consist of precisely-built, long trapezoid earth mounds covering a burial chamber. Because of this they are a type of chambered long barrow. In some examples, pairs of smaller burial chambers lead off from either side of the central rectangular burial chamber, itself connected to an ante-room. In others the entrance is a false entrance with the burial chambers accessed laterally from directly outside. A third group have merely a single large chamber.
Tombs of this type are concentrated in the Cotswolds but extend as far as Gower and Avebury with some isolated examples in North Wales. Tombs of all three types are generally evenly distributed and it has been theorised that the design evolved over time. Severn-Cotswold tombs share certain features with the transepted gallery graves of the Loire and may have been inspired by these, with the lateral chambers and other differences being local variations.
Examples include Wayland's Smithy in Oxfordshire, West Kennet Long Barrow near Avebury, Wiltshire, Hetty Pegler's Tump, near Uley, Gloucestershire, and Belas Knap, near Winchcombe, Gloucestershire. In Somerset examples include Stoney Littleton Long Barrow and the Fairy Toot.
- Orientations of Neolithic Chambered Tombs in Glamorgan and Gwent, South Wales by Martin J. Powell