I’ve spent more nights than most scholars looking at Roman fortifications, and they’re a masterclass in engineering. They layered stone and concrete, built a core of rubble for weight, and then faced the exterior with tightly cut ashlar. The mortar wasn’t just filler—it was a hydraulic lime that hardened underwater, which is why many of their walls still stand. Their towers were strategically spaced, allowing defenders to overlap fields of fire. If you can learn to blend that kind of material science with modern techniques, you’ll have a defence system that not only resists the enemy but also the march of time. The Romans didn’t just build walls; they built time capsules of durability.