Standing beside the folly walls,are a real cannon(it weighs a ton,I couldn't so much as move it) and Ron,an historian/archaeologist/gardener,who was clearing the site,as I arrived,and apparently has been given the painstaking task of clearing the area.He advised(and I've had it confirmed elsewhere in Porthmadog since)that a TV crew and historian visited the site recently,examined it in minute detail and assured themselves that it is ,in fact,Castell Deudraeth,first constructed in the 12th.century.The remains of an apsidal tower was observed.The cannon barrell(no mounting lugs) is to be somehow incorporated in the folly,when time allows.
see http://www.ecastles.co.uk/walesgr.html
see http://cy.wikipedia.org/wiki/Castell_Deudraeth