Wolfgang, I think Metchosin is right on the explanation for "capital". In latin, for what I know, the first meaning of "caput" is "head" ,and "capitalis" is " regarding the head " also metaphorically speaking, the first thing, the most important. Sometimes in ancient italian chronicles you could find the death penalty called "la pena del capo", the punishment of the head, even if the way of execution was not the beheading.