Columbia subject headings:
Nature conservation--Wales--Gwent.
Water-saturated sites (Archaeology)--Wales--Gwent.
Wetlands--Wales--Gwent--History.
Harvard subject headings:
Gwent Levels (Wales)--Antiquities.
Gwent Levels (Wales)--History.
Nature conservation--Wales--Gwent.
Water-saturated sites (Archaeology)--Wales--Gwent Levels.
Princeton subject headings: