In this image you can clearly discern the mound/motte,overgrown as it is.For a fuller explanation of this enigmatic image,see http://www.castlefacts.info/contentpages/castledetails/castledetails.asp?country=England&countyid=15&county=Essex&castleid=1189&latitude=51.6839790344238&longitude=0.661220014095306&uin=11160
NB:To me,the site is Saxon,as it lies astride the peninsula twixt the rivers Chelmer and Crouch,whilst Rayleigh Mount,known to be Saxon,being one of four motte and baileys built before the Norman Conquest,controlled the peninsula,twixt rivers Crouch and Thames,with Hadleigh,given Royal support,marshalling the Thames Estuary.
see http://www.pastscape.org.uk/hob.aspx?hob_id=380934&sort=4&search=all&criteria=purleigh%20mount&rational=q&recordsperpage=10
see http://unlockingessex.essexcc.gov.uk/uep/custom_pages/monument_detail.asp?content_page_id=89&monument_id=24680&content_parents=48