The richly ornamented three storey south porch and imposing tower certainly preside over the Market Place with all the grandeur of a cathedral, and the interior is just as astonishing.
Roman Cirencester (Corinium) had become the second most important town in Britain, and by late Saxon times there was already a very large church here. By the early 12th century Cirencester had an Augustinian abbey, and it was at about that time that the first church on the site of St John's was built.
Parts of it survive in the present church, most of which dates from successive renovations and additions throughout medieval times. So, for example, the Lady Chapel dates originally from 1235'50, the tower from around 1400, various chantry chapels from the mid 15th century, and the porch from about 1490.
The nave was rebuilt between 1515 and 1530, acquiring the soaring, slender pillars and huge Perpendicular clerestory windows that are such key elements of the church's light-filled, elegant interior.
It seems hard to believe that, little more than 100 years later, this glorious building was a temporary prison for more than 1,000 citizens of Cirencester, who were locked up here overnight by the Royalists after a Civil War battle in 1642.
Of the many interior features worth seeking out, don't miss the exquisite fan vaulting, or the wineglass pulpit, a stone masterpiece of about 1440 with delicate openwork tracery and decorative paintwork in burgundy and gold.