Looking at the construction site photos makes me wonder, might it not be better to build The Line as a 150-meter-deep trench instead of a 150-meter-high wall? I suppose all that excavation might be even more expensive than the high-rise construction, but I've seen enormous mining equipment already in use elsewhere that appears up to the task. The excavated rock might be useful as ore, or be crushed up to alleviate the worldwide sand shortage, or used to build new artificial islands or pyramids or pyramid-shaped islands. Meanwhile, The Trench would be easier to cool, less obstructive to migrating birds, and highly defensible with a few dozen turbo-laser towers should anyone attempt to fly along it in a one-man fighter to reach the small thermal exhaust port.