 The castle was located slightly away from the main road , to give additional space for the earthworks involved , and was positioned as to benefit from natural springs running down from under the hill . It had a motte and bailey design , with a 40 foot ( 12 m ) high motte , and a bailey around 500 foot ( 150 m ) by 300 foot ( 91 m ) , enclosing 0 @.@ 6 acres ( 0 @.@ 24 ha ) acres . A double bank and ditch ran around the whole castle , with both sets of ditches filled with water . In total , the wider earthworks occupy around 11 acres ( 4 @.@ 5 ha ) . A fossarius – a specialised ditch digger – was recorded as being employed maintained at the castle in 1086 . 
