I'm struggling with this thread (even without the diversions). Presumably the hole could have been:

(a) always there and used in some way in the original construction
(b) always there but not relevant to the original construction
(c) made later and used in a putative re-structuring of the site
(d) made later and nothing whatever to do with any later re-construction?

Is the hole important? If the hole is important, I would have thought it would be essential to evaluate whether it was made with metal tools or otherwise.

Also, I have to agree with Tiompan that more likely explanations (e.g. that the structure is largely as it always was, including a single chamber, and that some bits have subsequently slipped or fallen down) would need to be properly discounted before less likely explanations were seriously considered.