This section of wall collapsed in 1872,revealing part of an earth mound upon which the castle sits.It was not investigated at the time,but recent archaeological excavation has revealed that the mound is much older than the castle,suggesting that this could have been a Saxon lord's manor house before the Norman Conquest.
see http://www.castlexplorer.co.uk/england/eynsford/eynsford.php
see http://www.staykent.co.uk/tourist/Eynsford-Castle.html