It forms a barrier across an open chalkland ridge, bounded near Fulbourn by marshy fenland and near Balsham by 90-metre-high formerly wooded hills ("The Ambush").

[2][3] At Mutlow Hill the dyke runs beside a Bronze Age barrow dated to 2000 BC, which contained eight urns with cremated human remains, and which was reused in the Roman period as a shrine.

[3] In later Anglo-Saxon times, the northern part of Fleam Dyke was also the boundary between Flendish and Staine Hundreds (county subdivisions).

Fleam Dyke is one of four substantial earthworks, each a high bank with a ditch on its southwest side, running across the chalk downland ridge that carries the Icknield Way (and the Roman Road) across south Cambridgeshire.

Malim (1997) notes that Fleam Dyke experienced at least three phases of construction and thus had the most complex history of the earthworks, and suggests this could be "because it was built, taken, then retaken and refortified a number of times during the fluctuating fortunes of war during the Dark Ages.