 Holwell Castle , at Parracombe , was a Norman motte @-@ and @-@ bailey castle castle built to guard the junction of the east – west and north – south trade routes , enabling movement of people and goods and the growth of the population . Alternative explanations for its construction suggest it may have been constructed to obtain taxes at the River Heddon bridging place , or to protect and supervise silver mining in the area around Combe Martin . It was 40 metres ( 131 ft ) in diameter and 6 @.@ 2 metres ( 20 ft ) high above the bottom of a rock cut ditch which is 2 @.@ 7 metres ( 9 ft ) deep . It was built , in the late 11th or early 12th century of earth with timber palisades for defence and a one or two storey wooden dwelling . It was probably built by either Martin de Tours , the first lord of the manor of Parracombe , William de Falaise ( who married Martin 's widow ) or Robert fitz Martin , although there are no written records to validate this . The earthworks of the castle are still clearly visible from a nearby footpath , but there is no public access to them . 
