Hey everybody, very interesting. I would like to see a picture of interior jettying if anyone has one. I'm not sure what you mean but If i am thinking of it right it would occur for the same reasons for exterior jettying: to create different space from that below. I am going to speculate on the exterior jettying of middle ages.
It was a dark world with the Visigoths, Vandals, etc roaming the countryside. People huddled in cities for security if however disillusioned. The streets were there and residences were added. Now they typically did not build very tall so if you can't go up and up, go up and out. The jetty then did not interfere with street space, added more square footage, and created some security in closeness relating to strength in numbers, and the upper ground.
