The naming reason behind the rubble core method was quite evident once one knew about the technique.
But forming the rubble core did not mean the end of the wall's construction.
Far from, that might be actually the easy part.
As it could be done relatively easily given it was not done in winter, or more specifically during winters where the temperature dropped to zero, as the water in the slaked lime and slurry would freeze, halting the chemical reaction that would solidify the mixture and destroy the rubble core as the water would expand into ice.
But anyway, that small inconvenience aside, with the rubble core formed, then a veneer or shell needed to be formed around it, both to protect it, but also to give it some much-needed additional strength.
Because given the weak mortar used, and the core's asymmetric construction structure, it was actually unable to properly redistribute the forces acting against it, meaning it was prone to breaking if hit in its weaker points.
