dene hole

In archaeology, an artificial shaft that opens into double, trefoil (three-lobed), or double trefoil caves. These narrow vertical shafts were sunk up to 10 m/33 ft into the chalk rock of parts of Kent and Essex in southeastern England, particularly on the escarpment of the North Downs and near the Thames estuary.

The age and purpose of dene holes are disputed. Recent and possibly pre-Roman examples exist, and many have been identified as chalk wells or marling pits (for clay used as fertilizer). Other suggestions include such uses as hiding places from the Viking raiders, underground silos, or Neolithic (New Stone Age) flint mines.