Legend of Jakos
The Legend of Jakos is the semi-official origin story for the South Reach Emirates. It has been widely disputed by Arcadian scholars, but in the Emirates it is considered to be true. In fact, because it allows all five Emirs to trace their lineages to a single dynastic origin, it is the foundation of the ancient oaths that bind them together. Thus it is illegal to spread any alternate origin stories that dispute existence of Jakos and his sons in the Great Cities.
According to the legend Jakos was a man of purest and noblest blood, descended directly from the gods, but impoverished by circumstance. He had five sons, but no inheritance or legacy to leave them. In desperation he ventured deep into the deserts of South Reach in search of fabled treasure under a Sacred Mountain. Instead of a chamber full of treasure however he found a cave that contained nothing but a cursed trinket.
Said trinket was inhabited by a powerful Efreeti who for millennia has been luring treasure hunters and adventurers to either be devoured or bound into eternal servitude. Jakos however was able to outwit the demon and instead forced it to grant him a wish. Jakos wished for his sons to inherit great wealth, power and have an ever-lasting legacy. The Efreeti then split the mountain in half allowing the underground waters to flow onto the surface and create the Great Rivers, which made the unforgiving land flourish.
Jakos' five sons founded five cities along the river banks or in their deltas, which were named after them, and became the Five Cities of the Emirates.