Defilement

Ananke's weathered, wrinkly face grew dark. The old woman lingered for a while before saying:

"The other name for the Defilement is Corruption… a special kind of Corruption that appeared on the Great River and then spread from downstream like a plague. Or rather, was spread." 

Nephis leaned forward a little:

"Spread… from downstream?"

The old woman nodded heavily. 

"Yes. It is because the Defilement… its origin is the Estuary."

Her cloudy eyes grew distant. 

"The Seekers were always trying to reach the Estuary, traveling further and further downstream. But none of them succeeded in finding it. Eventually, they built a city of their own in the far reaches of the past — a city called Verge. Its grandeur could compete with the bustling prosperity of the large cities ruled by the sybils, and from there, they continued their search. Until, eventually… one of them really managed to enter the Estuary."