see http://www.dyfedarchaeology.org.uk/nevern/nevern.html
see http://www.welsh-cottages.co.uk/pembrokeshire/neverncastle.php
se
e http://www.cambria.org.uk/nevern/neverndigdiary.html (lots of images from the recent dig)
NB:Important.It may seem crass or stupid to us,but a lot of Welsh castles although built in stone(slate usually)were constructed without mortar, because they did not have the knowledge of how to make mortar, so instead they used clay.A severe downside to this approach is that,over time,rainwater washes out the clay infill(mortar) resulting in structural collapse.This is most likely what happened here.