Fens, the

Level, low-lying tracts of reclaimed marsh in eastern England, west and south of the Wash, covering an area of around 40,000 sq km/15,500 sq mi, about 115 km/70 mi north–south and 55 km/34 mi east–west. They fall within the counties of Lincolnshire, Cambridgeshire, and Norfolk. Formerly a bay of the North Sea, they are now crossed by numerous drainage canals and form some of the most fertile and productive agricultural land in Britain. The southern peat portion of the Fens is known as the Bedford Level.

The first drainage attempts were made by the Romans. After the Norman Conquest an earthwork 100 km/60 mi long was constructed as a barrage against the sea. In 1634 the 4th Earl of Bedford commissioned the Dutch water-engineer Cornelius Vermuyden to drain the Bedford Level, introducing Dutch drainage methods to the Fens.