There is an ancient curse upon the Athos Highlands that causes Humans to mutate if they break their personal code, or from having no code at all. What's worse, the mutations are permanent and even heritable. Some develop horns, tails, tusks, claws, pointed ears, or grotesque mouths on their stomachs. Those who never change their ways develop more and more mutations, and eventually to madness. A Human (Mutant) with enough mutations can even become a Beastman. The curse afflicts an area as far as the western faces of Heston, and as far east as Terebinth, to the northern reaches of Redfenland County. Vergister is famously beyond its reach, and its people are viewed as outlandish on that basis.
Historical records seem to indicate that before The Reign of Eld, there was no curse. It is prophesied that Arthur Pendragon will someday return to renew his reign and end the curse, if only the people remain faithful. For a century after his reign, the curse of sin created many mutants. In an attempt to bring him back, a mutant pogrom was enacted. More lenient kings since have eased the punitive measures on mutants, on one or two occasional due to transforming themselves.
As the curse doesn’t range beyond the realm, travel abroad is seen by some as as a way to 'get away with' things. Equally, the rest of the world is regarded as a place where anything could happen. The curse is seen in Orchalannon as a safeguard against wanton or dastardly behavior. Outsiders are regarded with suspicion, but may come to be accepted after remaining human for some time. One helpful side-effect of the curse is that it has a tendency of cowing enemy forces. What soldier would want to occupy a cursed land that could turn them into beasts?