There are three different period camps superimposed on each other. Camp 2 is the better preserved and is built within the confines of Camp 1, which is older. Camp 3 is only barely perceptible inside of Camp 2.
See:
http://www.pastscape.org.uk/hob.aspx?hob_id=17308
http://www.pastscape.org.uk/hob.aspx?hob_id=914187