Cyril Fox thought Black Ditches was the most easterly of a series of five earthworks that defended the East Anglian kingdom of the
Wuffings along the
Icknield Way, the others being collectively known as the Cambridgeshire Dykes -
Devil's Dyke,
Fleam Dyke,
Bran Ditch and
Brent Ditch. It is not as well preserved as the western defences. A small excavation in 1992 found that the Black Ditches had a ditch on either side of the bank. Only Iron Age pottery was recovered in this excavation. The total length of the ditches is around stretching from south of Cavenham towards
Icklingham, although there is no evidence of the ditch crossing the
River Lark at Icklingham. The Icknield Way crosses the line of the ditch towards the central area. In this area the ditch is generally no longer visible. The northern section of ditch remaining is around in length running across the eastern edge of Cavenham Heath towards the River Lark. The section is less well preserved, although up to high and wide in places. This section is not designated as an SSSI although it lies on the boundary of the Breckland Farmland SSSI. This section lies entirely within the parish of Cavenham. The southern section of the ditch is long, extending southwards in some form across Risby's Poor Heath. This section forms the boundary of Cavenham and
Lackford parishes before it enters
Risby parish to the south. ==Plant and wildlife==