The bastion in the wall of the Hall Gardens is made from locally sourced Cornbrash or Great Oolite limestone, the same stone was used to build the fabric of Peterborough Cathedral with dressed stone on the outside.
There are other examples of the stone in some of the oldest buildings in the town. A good example being 52 High St East, which is a Mediaeval Hall c1450, refurbished in 1660 if my memory serves. The stone contains the fossilised remains of bivalves, brachiopods and serpulids. It is a mud stone which in Rutland never exceeds 4.58m in thickness. The lower part of the bed is very oyster rich. It is from the Jurassic period so is between 145 to 200 million years old.
There is no written evidence of a town wall as all records from the period before the 19th century are in the vaults of the three families who owned the town. Anecdotal evidence is non existent but looking at the wall facing south from Hall Gardens and the fact that it has been cut into, to build the Hall on Norton Street would suggest it predates that building.
It is built from the same stone as 52 High St East so may be related to or date from the same period as that property. Professor Alan Rogers also shared the view that there was potentially a wall around the town. I would agree with that supposition bearing in mind the strategic importance of the town as the crossroads of two major east west/nor south roads. The very substantial formation of the walls at the junction of South View and Queen Street would suggest a robbing of older stone. The wall on North St West also looks similar in style and stone to the walls on South View.
All in all I believe there is sufficient evidence to warrant an investigation in the future by experts in the field.