There have always been rumours all around the Threetowns about the "Day of the hollow Sun". From what you have gathered you know that long ago, Arioch and his minions have tried to take over the towns. A mighty Necromancer and Priest, Dravin Rathul, aided Arioch in taking away the sun over the Threetowns. This phase of darkness lasted for many days in which the evil forces lead by Arioch himself tried to take over the towns and extinct all its inhabitants. Thats all you could find out there is no reference whether Arioch was stopped. You also have some doubts if this has happened, or if it is a prophecy... There is a small underground cult that worships Dravin and his vision of the sunless sky. They are persecuted by the authorities of course, but somehow seem to be able to settle in some faraway corners of the towns and even harata.