It is a rare thing to find the ruins of a medieval building inside prehistoric earthwork remains, but there is indeed the remains of a twelfth century church in the middle of the Knowlton Ring (or Circle) which is from the Bronze Age.
The famous antiquarian William Stukeley studied the place and was told by the locals that there was originally seven churches there and that six had just completely vanished entirely. It is understood that the people likely mistook the prehistoric banks and ditches as churchyard walls, as there is only evidence for the one. It completely went into disuse by the 1650s and was in a total ruin by 1730, when it's bell was taken and moved to Sturminster. According to legend, this was theft and tales have sprung up around the bell's removal from the old church.
Some had it that whoever stole the bell re-shod their horses hooves backwards so that their tracks could not be followed in the snow. Another local rhyme declared: "Knowlton bell is stole and fallen into White Mill hole." The hole is a deep place in the bed of the Stour, by White Mill Bridge at the approach to Sturminster. By the mid 19th century, the story was that the robbers were overtaken by angry Knowlton men at the bridge, and they threw the bell into the river rather than give it back. Three times the Knowlton men tried to drag it up but the rope broke each time.