one of the flimsiest parts of this premise is the "why are 'basements' a mezanine half way underground" - yes because mud flood
haha, which is very silly, because mezzanine basements started to be put into buildings at teh same time as the invention of central heating systems on multi-storey buildings... you need them to have windows for fire to actually burn, but better they are not where you open out to when you climb the half storey steps to the antre
they are also good places to store casks of wine and whiskey, indeed, when they devised the pressure-resistant beer barrels, then they could put them under the floor of the bar, only a half-storey step upstairs, without having to carry the casks upstairs, but rather down, and even today you see this in many 19th century era cities the bars have trapdoors where the beer barrels are passed downwards
also, they served other functions too, like in Bulgaria, even today, the mezanine basement floors are used in several parts of Sofia for "squat shops" where the shopkeeper is standing half a floor down selling stuff so you have to squat to use them.
