The dyke as it stands in its current form is a Romano-Britsh defensive earthwork. However H.C. Bowen in the excellent book “The Archaeology of Bokerley Dyke” gives a good argument for a much earlier origin. He argues that in the Bronze age the dyke was a cultural boundary which can be shown by the differences between types of round barrow which only occur either side of the ditch.
The bronze age date has also been partially confirmed by excavated finds, the similarity of Neolithic long barrows on both sides of the dyke show no significant difference in typology / culture at that time. There are problems with finds because of the confused stratigraphy caused by the different stages in the developement of the dyke. It was greatly deepened and heightened at a later stage of its history.