scaling ladders were conventionally pushed away or sidways with a pole. usually a short one to start and a longer one once it was away. Same technique we still use to raise tall building walls and truss's. took some effort to go straight out, sideways not as much. Problem I have with the theory, is all of the info I've seen was the pole was forked, so you could put it against something on the ladder. Would be very hard with a pole. I'm not sure of the slope on an earthwork fortification, a ladder would be more effective on a tall straight wall. If those are pikes, pointed on one end, and a 1 - 1 1/2 inch blunt end, I can't see getting them to stay on a ladder long enough to push it. My best guess is that an earthenwork fort has steep but possibly climbable slope and the pikes are purely an defensive weapon for stabbing, at a fellow using both hands to climb who couldn't defend himself. Better range untill he got in bayonet or sword reach. The headboard falls when the pikes are removed( eliminating something for the attacker to grab by rope or grapple and falling in the attackers face for encumberment) The failure in theis plan is like John said, why are so many outside the perimeter? You would have to expose yourself to get up and grab most of them. I thought initially they were to hold boards for the wall, and dirt piled on both sides, but the one does look like a pike, but it is inside the wall available for use. The other might or might not be the same thing.