What could be more prepping than building a whole stone castle? It’s the historical equivalent of a bunker for most part of modern (and ancient) history
Building castles to cover captured terrain was pretty common (unless of course there already was one around, in which case you besiege and take it, if you can). Of course, building a stone ond rakes time, so they'd build a temp one first, and then, ic theh manage to keep the territory, update it. So if it's prepping, it's a very common and prudenf version of it.
I wonder how many castles were built like codebases. Start with a little MVP and accumulate stuff over time that eventually gets refactored and eventually seems well thought out