SC—A number of authors have investigated these dykes, and concluded that they are pre-Celtic (of Neolithic age, constructed contemporaneously with Stonehenge and Avebury), and have nothing at all to do with defense or warfare. In particular, I would direct you to a book entitled Before the Delusion, by William Gleeson. In this case, he uses the vehicle of fiction (a novel) to present his arguments, which I find more compelling than claims that the dykes were built by Romanized Britons to stem Saxon invasions.
Sorry, but the surviving earthworks consist of two basic types — the oppida or hillforts, which are clearly pre-Roman, as Roman roads make course changes to skirt them, and these earthen walls, which cross and bury (here and there) Roman remains such as abandoned settlements and roadways. I liked some of the historical fiction (like “Eagle of the Ninth” and the related novels by that same author), but relying on them to relay reliable history doesn’t work.