The siege troops must cross the open ground in front of the city walls, a hard and open area where they are completely exposed to the long-range firepower of the defenders, vulnerable to ricocheting cannonballs and the whizzing of bullets, arrows, and darts.
However, when people are pushed to the brink, they can come up with all kinds of methods.
Sebastian Volbon, the engineering lieutenant colonel called to the road engineering headquarters, barely had time to settle into his seat before he was summoned back to the siege frontline. Cornered by two major generals, Lieutenant Colonel Volbon racked his brains and came up with an alternative plan: if digging trenches wasn't possible, then build walls - construct entrenchments on the ground surface.
In simple terms, this meant constructing corridors between two walls. Although this was far more labor-intensive than digging entrenchments, it was the only method available for the time being.