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
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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.