From the book Rule:

In my study of this world I’ve seen many uncanny and unknowable things stemming from the castles in the sky. These massive blocks cast shadows over towns, even cities but roam the skies impossibly and relentlessly as they hold to the course. The mad lords that rule them impose insane systems of government upon the people that live below them. The bright explosions when they come to blows with each other or wreak devastation on the lands below that disobey them impress and awe. Those that rose up to oppose the castles still inspire others to this day. Yet there are those who managed to remove themselves from the influence of the castles. These I sought to find but learned little of, those of the Hidden Green Wilds.

Not much is known of the Green Wilds tribes, the Keepers as they call themselves. They were an oddity in a world full of the uncanny. Their people would occasionally dislodge from the wilderness of the northern Hidden Green Wilds and come down to some small villages for trade. What they bartered away, as if it held little value for them, was always the finest silver veins and uncut raw gems of ostentatious size. Their causal trade in these valuables for simpler things such as well forged iron tools, large supplies of salt and the occasional southern grown herb or spice added to their mystery.

These displays of wealth also brought unwanted attention, but those parties that ventured into the green wilds to find the source of the Keepers’ wealth were rarely heard from again. Those that made it back spoke of nothing but endless wild country and harsh winters. Rumor and speculation surrounded them as well as a fair bit of invention, that they were in fact wild creatures themselves changed to men so that they might treat with man. Absurd imaginations of simple folk, but persistent in their retelling. I often wish Method were here to simply disabuse them of these notions.