Problem: monasteries, almost in spite of themselves, usually become rich and are nearly always populated with people professionally useless at defense. Solution: build. I found it staggering when I learned these places, islands... no, time machines.... from the Middle Ages and even earlier still exist and function unchanged in any real way. Even they don't know the treasures which may lurk in their libraries. They've survived this long, and presumably they will continue to do so. A good thing.