This is a fine example of an exceptionally large pot quern recently found in a 14th century foundation at the Westgate Centre in Oxford. It is made from probable Quarr stone from the Isle of Wight, supplies of which were exhausted during the 13th century.
Pot querns comprised two stones, the larger base (as here), and another smaller stone which was rotated inside it. Grain would have been fed through a hole in the centre, which also contained an iron spindle, and the grain would have been processed into flour between the two stones. This quern originally had two handles and a spout, typical features of pot querns.
Pot querns are not common finds and are typically associated with ecclesiastical and/or urban contexts. At 72cm diameter, this example is significantly bigger than its closest counterpart (at 57.5cm) and twice the average size for pot querns. It’s therefore unique.