▁them . ▁ ▁When ▁the ▁castle ' s ▁outer ▁walls ▁were ▁eventually ▁bre ached , ▁the ▁def enders ▁retre ated ▁to ▁the ▁relative ▁safety ▁of ▁the ▁keep . ▁It ▁too ▁with stood ▁the ▁efforts ▁of ▁the ▁sie ge ▁engines , ▁and ▁once ▁again ▁John ▁turned ▁to ▁min ing ▁to ▁bring ▁down ▁the ▁walls . ▁The ▁mine ▁was ▁d ug ▁beneath ▁the ▁south - east ▁corner ▁of ▁the ▁keep . ▁A ▁letter ▁sent ▁from ▁Ro chester ▁on ▁ 2 5 ▁November ▁offers ▁insight ▁into ▁the ▁methods ▁of ▁medieval ▁sie ge craft . ▁John ▁ordered ▁Hugh ▁de ▁Burg h ▁to ▁" send ▁to ▁us ▁with ▁all ▁speed ▁by ▁day ▁and ▁night ▁forty ▁of ▁the ▁f att est ▁p igs ▁of ▁the ▁sort ▁least ▁good ▁for ▁e ating ▁to ▁bring ▁fire ▁beneath ▁the ▁tower ". ▁The ▁wooden ▁props ▁supporting ▁the ▁tunnel ▁d ug ▁beneath ▁the ▁keep ▁were ▁set ▁al ight ▁to ▁collapse ▁the ▁mine , ▁bringing ▁down ▁one ▁corner ▁of ▁the ▁keep . ▁Still ▁the ▁g arrison ▁held ▁out ▁and ▁sought ▁safety ▁behind ▁the ▁stone ▁partition ▁or ▁cross - wall ▁in ▁the ▁keep , ▁abandon ing ▁half ▁the ▁building . ▁The ▁Bar n well ▁chron ic ler ▁remarked ▁that ▁" for ▁such ▁was ▁the ▁structure ▁of ▁the ▁strong hold ▁that ▁a ▁very ▁strong ▁wall ▁separated ▁the ▁half ▁that ▁had ▁fallen ▁from ▁the ▁other ". ▁ ▁Cond itions ▁within ▁the ▁keep ▁w ors ened ▁by ▁the ▁day ▁and ▁the ▁g arrison ▁were ▁reduced ▁to ▁e ating ▁horse ▁flesh . ▁In ▁an ▁attempt ▁to ▁reduce ▁the ▁demand ▁on