Until the construction of Bridgwater House in the 1970s there was a three meter length of stone wall at the junction of King Square and Chandos Street. This was assumed to have been part of the castle, as by Parker in 1856. [1] This fragment corresponds with the corner of ‘Castle Garden’ on Locke’s eighteenth century map.
Whether this was an original piece of the castle, perhaps part of the wall between the inner and outer baileys, or a later rebuild using castle materials is unclear. There are certainly several known examples of the reuse of castle materials nearby, such as in the cellars and garden walls of Castle Street and King Square.
However, these mostly consist of just red Wembdon sandstone, whereas the few rare pictures of the piece of suspected King Square castle wall show a mix of sandstone and blue lias stone, much like the surviving wall on West Quay.
[1] Parker, G., ‘Proceedings of the Congress’ in the Journal of the British Archaeological Association (Vol. 12, 1856) pp. 376-377.