Witches are are powerful individuals with a knowledge of magic, and are respected and feared throughout the empire, which is divided up into to many competing states. However, magic is slow and requires many steps which require a great deal of length. Witches are also small in number. This makes them a potential target for assasdination, and requires them to have bodyguards to protect them. Due to their value to the empire, witch society exists as a semi-independent entity that conducts it's own affairs and takes remains separate from the various governments of the countries.
I've built witch society to mirror the religious city state of Rome, a long ago autonomous region in a kingdom known as the Holy Roman empire. This empire was made up of a confederation of countires, similiar to the EU of today, with the Pope of Rome at the "head" of its faith.The problem is that Rome kept getting invaded by everybody. You don't like something the head honcho said or did, or he refuses to crown you king or grant you a divorce from your wife, invasion. Rome has been seized and occupied by enemies so many times that it is hard to come up with an exact number.
Clearly being at the head of the mainstream religion wasn't enough for leaders to respect it's autonomy. I need a way for witch society to remain protected from the ongoing wars that occurs between nations. However, putting the state in some isolated mountaintop or desolate wasteland doesn't work, as they cannot retain the influence they have in the political games and lose their value. I need a (non-magical) way to accomplish both goals.