How would castles be designed in a world where magic exists. Magic has the following rules:
- All magic requires runes and a verbal activation (saying 'magic words' that correspond to the runes)
- Any spell lasts a maximum of one minute (no enchanting)
- Any spell has a certain maximum amount of power, and will not complete tasks under that power (you can create a small fireball, but can't make a storm or teleport)
- Any spell takes three seconds to take effect after the verbal component has been said (gives time for a counter-spell)
- Runes can be traced on a surface (temporary rune) and can then be activated only by the maker, or engraved/written (permanent rune) where they can be triggered by anyone holding the object.
- All activation phrases must be yelled, and cannot be muffled (can't use magic while gagged or holding cloth over face)
I want to know how castles would probably be designed, given that this type of magic exists, and is fairly accessible, although normal troops would likely only know a few spells, mages who know thousands would accompany every army and defend every fortress.
Magical firearms don't exist yet (no one invented them at this point) but magical self-loading crossbows have been invented and are common, although loading a trebuchet is out of the reach of a single spell.