The Lamp of Sylvania
The reason for Nemaucum is the crossing it controls. The Loing is a “secondary” river. It is not navigable except by small boats. Individuals can small groups traveling cross country can often cross such a river at a ford, or even swim it, but cargo and wagons, and such travelers as merchants, require a bridge or ferry.
The Yonne is a larger river, and they reach it after traveling most of the next day, a damp, dreary day on the road. The bright side is that the Orcs don’t like to bother running around in the rain. It’s a safe day. But they don’t cover ground as efficiently as they can. They are forced to make camp on the bank of the Yonne, in a stretch of land devoid of settlement.
Well, currently occupied settlement, at least. They can see several old ruins nearby, along the river.
According to Marcellus, an old religious commune, or study place of some kind. He’s never been there. The terms he has with Redscratch cover just travel. He’s never pushed his luck with diversions for exploration.