Recently a magical wall has appeared along a 200 mile stretch of the River Yol, stretching from the Troll Fens in the north, to Phostwood in the south. It is 30' high, and extends to the bed of the river.
This appeared during a massive unnatural thunderstorm, which affected only the river.
The wall was created by the Theocracy. The details are unknown. The Theocrat had previously made an offer to the Duke to create the wall, in exchange for significant tribute. The Duke had declined, which in hindsight was a wise choice because a means to invade the Duchy through a tunnel under the river had already been put in place.
The presence of the wall is a reaction to the influx of refugees to Albarg, especially from Paltrave.
The wall appears lethal to humans and demi-humans. Animals and humanoids seem unaffected. Hrrtigor confirmed that he and his people had regularly crossed the river since the wall had appeared.
The wall has closed the border for now.