Arbury Banks is one of six Iron Age hillforts on the Hertfordshire chalk scape from Hexton to Royston that also includes Wilbury Hill Camp at Letchworth. Arbury means "earthen fortification". It was probably built during the late Bronze Age. The site probably contained houses, stockades for animals, or pits to store grain. It is not known if the site was defensive or just an enclosure for animals, to store food or for rituals. The site is now a Scheduled Ancient Monument.
The monument includes an Iron Age hillfort situated on high ground near the Newnham Way, 1km south west of Ashwell parish church. The monument measures 290m north east-south west by a maximum of 245m north west-south east. The defences consisted of a ditch with an internal bank. The ditch, although no longer visible as an earthwork survives as a buried feature and is visible on aerial photographs and as a soilmark. It measures an average of 5m in width and is infilled along its entire length. The internal bank survives only intermittently and measures a maximum of 2.5m in width at its top and survives to 1.2m in height at the south western end of the site. Two causeways give access to the monument, one to the NNW measures 20m in width, the other to the SSE is about 40m in width. The interior of the monument contains features which are visible as cropmarks and on aerial photographs. These marks represent rectangular, square and curvilinear enclosures, hut circles and pits which survive as buried features.
An excavation of the defences by J Bedlam in the 1850's found that the external ditch around the hillfort measures 6m in width and 4.5m in depth. The fence is excluded from the scheduling though the ground beneath it is included.