The Importance of Skilled Work in the Norman Conquest

I don't think the sources are clear enough for us to know whether any of the labor was forced or not. I suspect in the circumstances of the Norman conquest that some of the maybe quite a lot of the grump work could be done by forced labor. So there's no reason to exhaust your garrison. You can see from their spiral staircases and the intricacy of their layout, these are well thought out, well designed buildings. The other thing, of course, is you need someone to design it all for you.