When most of the population is united under one Kingdom there is no room for an inadequate king. To ensure that each heir is fit to rule and no bad seed would destroy the flourishing empire, a challenge was introduced to test the heir.
The challenge of Ebrado.
It is executed by an untouchable and mysterious cult; the Quillium, and it has shaped history by deciding which heir was to rule, binding the royal family to a tradition which grew ancient over the many kings.