It's called "hoarding", a temporary wooden construction that would do two things.
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Add lots and lots of shooting positions without making lots and lots holes of in your brick wall.
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Make it possible to drop rocks straight down on enemies who are at your walls.
The very obvious downside is that instead of having a thick wall between you and the enemy, you've only got a wooden board there. That's fine if they're shooting arrows, not so much against siege weapons or large guns.
So the hoardings would usually be empty, except during an assault, the logic being that you're going to die anyway if you lose.
Side note: since these were temporary, I doubt they would have had baked roof tiles on them. Maybe it's a kind of fireproofing, which was definitely an issue? It takes a lot of work to lay tiles though.
This missile is only "Intercontinental" if you launch it from the edge of a continent. It's got about 6000km of range, which is a lot, but these are obviously meant for use in Europe. They were probably thinking of London and Paris when designing them though.