The ancient largest North American city deserved to be ruled by no less than a deity, or a descendant of it, so the purity of the bloodline was of paramount importance. The Cahokian Royal House went to great pains in order to preserve it.

And it was not an easy task. Who could prove beyond any doubt that the son of the mighty Ruler was, indeed, the progeny of his divine father? After all, no DNA tests were invented just yet.

Well, those Cahokians did not go quite as far as the Ptolemies of Egypt by marrying the royal heirs to their full-blooded or half-blooded sisters. Nevertheless, they’d found a way to ensure the required purity. The full-blooded princesses were useful in more than one way, as it turned out.

The precious blood could be diluted, but to a certain extent. So the royal heir would be married off to whichever mortal noblewoman took his fancy, permitted to make children and live happily forever after. But his children would not ascend the throne, however frustrated they may have been feeling about it. No mortal woman, as chaste as she might appear, could be trusted with delivering a pure blooded next ruler. Women were too difficult to guard throughout their fertile years. There was no way to ensure the paternity of her child.

So was the Cahokian ruling class frustrated? Not at all! The solution was simple, as long as the royal family did not run out of princesses. Only a son the full-blooded Cahokian princess would be allowed to ascend the throne.

And so the ruler would rule contentedly while his sons knew that no amount of intrigue would place them upon the throne atop the glorious, ten-storey-tall Cahokian Mound. And all this time the lucky son of the Ruler’s Sister would rub his hands, getting ready to take the burden of governing upon his dear Uncle’s, sometimes hastened, death.