Among the Westerlings, monarchy is bestowed by the great goddess Rigatona, whose name means “great queen” and who is called Juno by the Ardeans. She is the power of mystical sovereignty, i.e., the right to rule, and is represented on earth by various orders of priestesses. In the ancient kingdom of Gatavia, like most Westerling kingdoms, there was a hereditary college of priestesses who embodied the sovereign power, it was through marriage to the heiress of the college (the youngest daughter of the previous ruling queen) that a chieftain of one of the clans would gain the right to be king.
When the Ardeans conquered Gatavia, the Westerling clans fought bitterly and without relent, even when such resistance had become futile. They simply would not obey laws that did not come from divine right. Finally, the victorious Ardean general who has seized the Brain of Bran came up with a solution, he married the heiress and became the lawful king. From his day forward, every Ardean governor of Gatavia, upon taking office, would ceremonially (or occasionally actually) marry the heiress and become de jure king of the province (although he would never publicly take the title as Ardean emperors endured no kings).
However, when the Ardean Empire converted to the Orthodox Fane (a predecessor of the Lawful Church), such pagan practices were banned. Many argue that this was one step in the failure of the Ardean Magical Defense that led to the Return of the Trolls and the rise of the Old Ones.
The priestess college was formally dissolved and the heiresses became fewer and fewer in number and harder and harder to find. However, Octavia of Maeve was the last of them. Yet Juno's promise to the kingdom was absolute, the line would never fail, and royal power would come from no other source. A great geas was lain on Octavia, she was possessed by one aspect of the goddess herself—Juno the Hag of Night---and doomed to haunt Hod until the questions be answered and her destiny fufilled.
The marriage and coronation must take place at Hod (the spiritual center of the ancient kingdom) on the 21st of December. From then on all soldiers who serve the King receive +1 (or +5%) morale, and any domain-related random roll made by the king as overlord is made twice with the king taking the better roll. The king also gains a magic resistance of 16+.
The king's rule lasts as long as the marriage does. The marriage can end with the death of either party or if the queen publicly dissolves it. If the king leaves the borders of Gatavia, or touches a dead body, or humbles himself in front of any mortal, he loses his royal power and authority until a suitable penance (set by the gods) is performed.