The concept behind this is that the old civilisations in my story had very funny gadgets that eventually ran out of power some centuries after their masters 'left'. The surviving civilisations dubbed them 'Autumn guards' because they are always buried under dirt and leafs and seem to 'guard' the areas they are reactivated in, which are mostly forests.
Since humans are still curious and still have shovels, they regularly bump into one of these guardians and attempt to reactivate them. It is not adviced to do this near any settlement because rift-powered hammers really hurt your buildings. Fortunately thats the only weapon they can still use since time took its toll on the ranged weapon systems.
Edit: Oh crap, frontpage? Thank you magical frontpage world!