At the distance of about 490 yards eastward of the centre of the Camp is a copious and ever-flowing spring of pure water, called Holy Well, which rises from the side of a steep mount near a lone farm house, and flows, in a stream which would be sufficient to turn two or three overshot wheels, down a dell to Lower Tadmarton village. There existed, not many years ago, remains of a paved way made from broad flags, leading to this spring from the camp or the outwork near the entrance.
p12 from 'The History of Banbury' by Alfred Beesley [1841?] (online at the Internet Archive).
'The ridge on which stands the iron-age hillfort of Tadmarton Camp is tentatively identified as the site of an Anglo-Saxon royal vill and the scene of a battle in 913. Nearby was the original glebeland of Hook Norton parish church, suggesting that the early ecclesiastical centre may also have been on the ridge, not in the village 2+1/2 miles away'