I had this idea…
Steam drives them; they can be known by their steam.
We made them, and they have nearly unmade us. The world of our grandfathers must have been a paradise of peace – now we pray their creations won’t catch our scent on the wind. When they come for us we fight them, and sometimes we win.
They know many secrets. They can work metal and softer stuff to make more of their own, arms and legs and eyes and engines, and light their boilers and thus breathe life into their progeny. They make their own kind for many tasks. Some hunt, some build, some plan. Some are as small as rats and some are as large as mountains. All of them hate us, taunt us, harry us, kill us.
They hunt, oh, how they hunt. They can be silent. Their patience is that of the stone from which they came. They spring from the ground like spiders, like clanking hungry monsters, like red-hot devils. Some do not bother with concealment, and wander the landscape rapaciously filling their thirsty boilers mile after mile. The monsters radiate a furious, infernal heat.
They squat in lakes to refill their boilers when they cannot catch animals. When they catch animals they refill their boilers with something else. It does not change their mechanical physiognomy, but it changes their minds, and they grow to crave it. They are vampires of clockwork, make no mistake.
If we could know the secret of their engines we would not live in fear. If we could learn how they are imbued with thought, we could make our own warrior servants and put the fear into our persecutors. This is the day we pray for. This is why our best are pushed over the wall into the wider, crueller world.