The 100 years old brick buildings don’t have any voids. That only started post-WWII when ventilation became a real concern.
But even then those houses are likely to have wooden floors and more modern drywall remodeling in some areas. My house is hurricane-proof but not rat-proof.
I guess Greek house building was several decades ahead of Belgian house building then, because I’ve yet to see a pre-war house with cavity walls. I guess the cheap coal heating and lack of a need for cooling must have something to do with it.