Welsh Arithmetic
At this point we must pause, and make a brief excursus into the Welsh laws. According to the laws, a primary division of the kingdom was the cantraef, literally one hundred townships. Each cantraef was subdivided into two commotes: each commote is made up of 48 townships. But, you will say, where are the missing two townships? These belonged to the king ; one was the King's Waste, or the Ffridd, and it was here that many of the castles were eventually built. The remaining township was the maerdref, or royal demesne. This had the best land in the kingdom, and it was here that the llys, or royal palace, was built.

Here we see a plan of the Gwynedd, showing its division into commotes. The site of Rhosyr is ringed.