For one thing, we don't operate at similar scales of human engineering. The Romans, for example, had huge armies. But the entire army was also experienced at engineering and building, to the point where whenever they weren't fighting, they were building fortifications and bridges, which gave them terrifying speed and technological superiority.

Build an army of construction workers, engineers and craftsmen today and you can build some pyramids. Hell, skyscrapers go up in China in like a month now.