Therfield Castle is a mid 12th century earthwork motte and bailey fortress, which possibly had a contemporary village enclosure. Completely disused by the early 13th century, this adulterine castle was probably built in the Anarchy in the reign of King Stephen. The bailey may have been slighted before its construction was complete and the small motte with its depressed centre dug in the 1920s, is partly enclosed by a ditch. Excavated in 1958, the motte was found to be absent of any structures but the rectangular bailey was built with a timber-revetted rampart. In 1960 most of the earthworks in the bailey were levelled, leaving only wet ditches and low ramparts in the field boundaries, to give its layout. 3 miles east at Barkway is Periwinkle Hill and 10 miles south is Walkern Castle.