The original purpose of this map is to create a kind of "toll" bridge in some very old and overgrown ruins (an old capitol city in my specific case, which is why there are walls and disused fountains). The barricades on the bridge provide cover to the toll collectors, who will interact before any travelers get close. In my scenario, the river and overgrown pits were potential areas where hostile plant life could approach and attack anyone who was closest. The river contained additional hostile aquatic plant life, so one should avoid falling or being pushed in ;)