Carnford's existing walls had been repeatedly expanded and reinforced atop the original fortress. Tall and solid, they were enough to withstand any attack from the age of cold weapons. But times were changing. The Sauron not only possessed cannons—their casting and operational techniques were steadily improving as well.
The experiences of both Osric Fort and Eagle Nest had proven that traditional vertical high walls were not indestructible under sustained heavy artillery bombardment.
"We can't pin all our hopes on the city walls." Karl pointed to the blank area surrounding Carnford City on the sand table. "Outside the walls, we need to prepare a few 'appetizers' for the Sauron."
"First, beyond the existing moat, we'll dig at least two—perhaps even three—Z-shaped or zigzag reverse-slope trenches encircling the main city, according to the terrain. The trenches must be deep and wide, with sharpened wooden stakes and iron caltrops filling their bottoms. Between the trenches, we'll set up large numbers of chevaux-de-frise, caltrops, and traps. This will be the first killing ground we prepare for the Sauron infantry."
"Once they exhaust themselves filling in or bridging the first trench and think they've reached the walls, deeper and more intricate second and third trenches will be waiting for them. Our soldiers, meanwhile, can safely shelter behind the breastworks farther back and use muskets, Molotov cocktails, and explosive packs to harvest the enemies trapped in the trenches like whack-a-mole."
"Second, between the final trench and the main city wall, use the earth dug from the trenches, mixed with gravel, to ram down a low but thick and sturdy sloped earthwork. Its purpose isn't to stop infantry, but to absorb and deflect cannonballs."
"When solid iron balls strike a soft earthen slope, their kinetic energy will be greatly absorbed. They'll have difficulty ricocheting and will be