Disregarding the wall's thickness for the moment, consider carefully stacking a selection of flattish random stones horizontally, in courses, between two upright boulders, in a way that is well bonded and structural.
Now, consider using the same stones and this time stacking them vertically, wedging them securely against each other, between the same upright boulders which are spaced the same distance apart. Which wall do you think is stronger?
Which one couldn't you push down very easily? Which do you think would last longer? Which looks more interesting? Which would you vote for in an open walling competition?
I know the one I would vote for.