Penrhos Castle is a medieval earthwork motte and bailey fortress, possibly founded by John de Monmouth. The low motte encased by a ditch, stands on level ground and is defended by a powerful counterscarp bank and double wet ditches. The bailey with its surrounding ditch, is also defended by a northern counterscarp bank and double wet ditches. In 1248-52 in a private quarrel, William de Cantalupe, lord of Abergavenny probably dismantled the castle. 4 miles south is Raglan Castle and 8 miles west is Abergavenny Castle.