Celebrim
Legend
When considering the effect of magic on a world, it doesn't seem to make much sense to me to hew too closely to guides that were created to enable a game. Those guides are fine for what they are meant (suggestions on one way to run a world) but hardly are the bible of magic worlds and societies.
No, but there is no bible for magical worlds and societies. We can however deduce something about the 'typical' magical world and society by noting the following: "Castles exist."
This post is about a mental exercise: what would happen to castles if there was magic and monsters in the world.
Sure, and I've been happy to participate in that mental excercise. However, one problem with the mental excercise is that there is no bible for magical worlds and societies. So, lacking any standard, everyone participating in the mental excercise has made certain assumptions about the magical society and based his analysis on that assumption. And that's fine, but the answer you give is wholly dependent on the assumption.
I dont' have a problem with approaching the question in that way, but I personally prefer approaching the problem from the opposite direction.
1) We know magic exists as a given.
2) We know castle exist as a given.
What is the magical society like given those two facts? What's important about this approach is that almost everyone assumes #1 and #2 first because they are the standard tropes of the setting, and only afterwards starts thinking about whether #1 and #2 are incompatible. Some people here seem to want to give the answe, given #1, #2 must be false and they proceed to then invent the conditions for a magical society where this is true. But, those assumptions depend entirely purely individual and utterly pliant opinions about the setting. None of them strike me as having nearly as much reasonableness as, "It's a standard fantasy, ergo castles exist." Therefore, I'm more inclined to say, "Given #1 and #2, what must the society and the magic be like to achieve this?"
Or more generally, what must be true about the magic of a magical society if the society in general superficially resembles historical periods of our own non-magical world.
A DMG may claim mages would be rare and perhaps they would be in the typical realm. But can you image a Rome or any other conquering power not exploiting something as potent as a mage?
You see this is itself an internal contridiction. Unless the society superficially resembles the historical periods of our own non-magical world, I cannot imagine a 'Rome' within it. If we don't assume as a starting point 'superficial resemblence to our own history and myth', and instead choose as a starting point, 'lots of magic exists', then the whole question becomes utterly unanswerable except to say that, "A society with pervasive magic would look nothing like our own history and myth, and would likely require the lifetime of a dedicated polymath to even begin to imagine what it would be like for a given set of assumptions about magic." And keep in mind, most of the really important questions about magic and its use aren't really answered by D&D RAW at all, and often are never even addressed by people who play D&D because questions like, "Can anyone with sufficient intelligence learn to be a wizard?", "How much experience do you get training to be a mage and simply practicing magic as opposed to overcoming lifethreatening challenges?", "What makes magic work?", and "What can't magic do?" don't really come up in most games because they are tangental to the standard goals of play.