Design weight may be small. But the dome is high and the area is empty. The load of the wind would be enormous. Therefore, the dome must be very strong.

I think you misunderstand.

It doesn’t matter what the dome was supposed to keep out, or not. What matters is, the dome has to support it’s own weight. Domes normally do this by dint of simply being an arch, across any vertical cross-section you could fancy selecting.

Even so, to build a dome whose peak is higher than a rather substantial looking high-rise tower _with radio masts atop it_ …. just there, just to hold itself up, that is an insane level of material strength there. We couldn’t do it today. I doubt we could do it even a hundred years from now. I’m honestly not sure the materials to build such a structure will EVER exist outside of science fiction.

Now factor in that a great big swath of the dome is simply gone. MOST vertical cross-sections of the dome are NO LONGER INTACT ARCHES. That bit directly over the center of the city? It’s only supported on one side. It’s probably been hanging there since the aliens left Earth behind.

We couldn’t do that for 1/10 as long, with a damaged dome 1% the size of that one. Literally, right now, that would be an engineering impossibility.

…

Thought experiment time: let’s say those panels are made of some sort of Aerogel – but with a closed-porous and hydrophobic surfacing treatment. That means it weighs little more than air itself.

Silica aerogel (Carbon and Graphene aerogels are much too porous, and would let the exterior in far too easily) has amass of 1,99g per cubic meter; if we presuppose a 1cm-thick pane (ludicrously thin, really), that’s about 1,900g per hundred square meters. Air itself weighs 1,200g for the same volume.

Based on the buildings, I’m going to guess at the dome being roughly a half-sphere, 1km in diameter (it’s not, it’s a bit flattened, but let’s keep the back-of-napkin math on the simple side, please!). That gives it a surface area of 1.26×107m^2 – or, 12,600,000,000 square meters.

Exclusive of any braces, struts,or other primary structure that means the panes collectively represent 126,000,000 cubic meters of material. That collectively weighs 239.4 million kilograms. To put that in perspective, a Nimitz class nuclear aircraft carrier has a displacement of roughly 92.2 million kilograms … a bit over one-third the weight of this dome.

An actual dome that size, made of the best and strongest silica aerogel we could manage, would collapse under it’s own weight … and do so long before it was completed as an actual dome.

It certainly wouldn’t leave a panel that must measure at least 300m on a side, dangling in the air, supported only along one edge, for a century or more.

…

So, like I said: the fact that the majority of the dome is still there at all – beyond, say, the lowest 20% around the perimeter of it – is testament to some Godlike-Amazeballs material strength. Maybe not Niven’s “Scrith” … but certainly closer to it than we can do aught but _dream_ of, ourselves!