Summary: Strange clockwork constructs emerge from the ground, consuming resources from an enchanted forest. The local druidic circle battles them, using a peculiar type of natural power.
The Thornwood was deep in the untamed wilderness, protected by the mightiest of druidic circles. The Circle of Thorns kept the woods clear of interlopers, protecting nature from civilization, just as often as protecting civilization from nature. The human empires of the continent rose and fell, but the distance and depth of the woods deterred even the greediest.
The Thornwood was not totally devoid of human inhabitation, though. The Thornwood protected a number of small villages and communities, largely populated by outcasts from the rest of society. They lived in heavily controlled settlements, managing their population and growth as to avoid the ire of the fey and fell beasts that lurked in the deep woods. From their wisest children were recruited the druids and their acolytes, such as Manoc the Mauler.
Manoc was a red-haired titan of a man, standing almost as tall as an upright bear. With a mind as strong as his muscular frame, he was able to wrestle the strongest animals of the Thornwood. The Circle of Thorns' leader, Mother Scathach, gave him the most difficult assignments. From slaying necromancers and their defiled dead to guiding wayward travelers to safety to protecting rare animals from poachers, Manoc accomplished them all with ease and expediency. Adept with sword, spell, and shapeshifting, Manoc feared no animal, abomination, or human.
One day, a villager came to the circle, telling Mother Scathach of a terrifying new threat from below. Clockwork constructs, built in the shapes of long-dead creatures, climbed out of artificial caves and tunnels far below the earth. They began to rip apart the earth in search of minerals, and attacking in their way. The animals bore the scars of strange weapons, if they were lucky enough to survive them. With steam and fire, they rose like a metal cancer from beneath the ground.
Mother Scathach did not know from whence they came, but she granted a quest to Manoc. He would have to descend into the machines' steel hive, and impart a spell at the heart of it. It would not be an easy undertaking, given they seemed innately hostile to any living thing that approached. Manoc observed the machines, and he planned his own strategy.
The Circle of Thorns, like other druids, largely eschewed metal due to its interference with the fey rituals they used. While using metal tools and weapons when necessary, they also avoided excessive use due to the rust monsters that inhabited the underground. Excessive use of metal would rile them up, and cause them to surge forth and blindly attack anything they found. While they slept certain seasons, Manoc saw fit to wake them early.
Manoc ordered the Circle to build fires and blow the smoke into their underground warrens, causing the rust monsters to stir a season too soon. He left trails of metal artifacts that pointed towards the machine-kin hive, which was part of his plan. The rust monsters had antennae that rusted the strongest metal armor in seconds. The powerful crossbows, flamethrowers, and stranger weapons of the machine beasts reduced the rust monsters' numbers, but not enough to totally destroy their numbers.
While the battle raged through the surface and tunnels, Manoc lead his team into the heart of the complex. He transformed into the shape of an innocuous rat, the sort of creature the machines did not bother with. He saw the underground foundries, where the machines made more of themselves. He saw the mines, where massive machines separated the ore and slag. He saw the massive array of gears and switches that housed the machines' memories and programs, their analog of instinct. Upon reaching the heart, he unleashed the spell.
Manoc saw the switches change into new configurations, but he did not have time to behold the effects. The remaining machines, having freshly defeated the rust monsters, descended upon them. The druids transformed into animals small and fast, leaving that clicking cavern behind. The walls seemed to close in on them, but they managed to escape to safety. Even one druid, whom they'd thought was left behind, had simply turned into a mole and burrowed out safely. The machines' complex, though, was not destroyed like Manoc thought it would be.
When Manoc informed Mother Scathach, he asked why her spell did not simply destroy the machines in a single swoop. The old woman laughed mirthfully, and told him to wait until the next season. While skeptical, the younger druid did. He waited the whole winter for signs of resurgent machines, but it was not until spring that he saw what she meant.
When the machines came out, their behaviors were modified. They no longer strip-mined the earth, but instead tended to it. They excavated small amounts of metal, but they also planted trees in their wake. While no longer mindlessly aggressive, they nevertheless defended themselves from attempts to harm themselves. The new machines also incorporated new alloys in their construction, more resistant to the rust monsters' abilities.
Manoc understood the Mother's plan: Now, the machines were part of nature. If their numbers swelled too much, the rust monsters would thin them. If the rust monsters swelled in number, the machines would adapt. Now the druids had domesticated the machines, or at least pushed them towards a less harmful path. That was how Manoc the Mauler became known as Manoc the Mechanic, founder of the Circle of Steel. To this day, it is said none dare enter the Thornwood without their blessing, for beast and machine alike defend it.