The original Oubliette could be used for anything including starvation and frequently was. A dungeon origin was the Donjon which was the function of the central defensive tower. I.e the White tower was a Donjon which also supplied security for the family. When families no longer felt the need for such security for themselves, the Donjons remained.Ummm, maybe. I thought an oubliette was for forgetting the prisoner until death? The one under the town-hall was for 'softening-up' prior to questioning. The execution places are elsewhere.