Who could build castles in the medieval times?

Answer 1

Well, I suppose generally anyone who had the money to hire laborers and pay for materials could build a castle. But given the great cost of building a castle in terms of raw materials, labor, and time, this typically meant that only kings and very wealthy and powerful nobles could actually do so.

If you're wondering if there were laws that expressly forbid peasants from building a castle or something to that effect, I have personally never heard of such a law existing, although honestly it would not greatly surprise me to discover a particularly paranoid monarch somewhere made a decree that specifically forbid peasants from building a castle. But such a law really was not necessary as no peasant would have had the means to build one even if he wanted to.

Although there probably was some legislation in place at certain times or in certain places to restrict the ability of a random nobleman to build a castle. For example I remember reading about Broughty Castle that fortification of the site began when an Earl was given permission to do so, presumably by the monarch at the time. Although this was in the mid 15th century, which is pretty late into the castle building era, so I am not sure if that was standard throughout the medieval ages or something unique to that century or to Scotland where that specific castle was built. In any case this sort of law would make more sense to me given that some nobles did actually posses sufficient wealth to build a castle and support an army to defend it, which depending on the noble's loyalties might have posed a threat to the other nobles in the area or even the local monarch.