The Norns

Around AD 950, three women scientists entered our dimension for another where technology had advanced easily 12 to 15 centuries further along. They easily surveilled the pre-electricity native cultures of the world. They found it startlingly identical to how their home world appeared many centuries earlier.
One hallmark of their culture was the human ability to band together against a common perceived threat, and then fall apart into petty bickering after the threat was gone, and then join forces again when the next threat appeared. In their early history as in ours many sea monsters and mythical beasts were alleged by possibly-intoxicated hunters and gatherers, and as rumors turned into tall tales, many loose associations of hamlets and villages turned into fortified city states either to defend themselves from human enemy armies and navies, or, sometimes, to defend themselves from a mythical threat which only existed in their imaginations. But centuries later after proper Science has been developed, how does one know which legendary threats were real?
That raised two questions, (1) if those pre-historic imagined threats had been treated with the Scientific Method to determine their veracity, would their civilization have progressed so quickly, or (ironically) would technology (particularly military technology) have wilted under better scientific understanding of their world? And (2) would their civilization have survived if those threats had turned out to be real?
The second question was what they hoped to answer by meddling in the history of this parallel world, this disposable copy of their world.
They gathered legends and myths which coincided with those of their world. They used their considerable genetic and electromechanical technology to build many of those man-eating monstrosities and set them loose into the environments per their legends to see what would happen.
The age of the man-eaters began.

Die Nornen Urd, Werdanda, Skuld, unter der Welteiche Yggdrasil by Ludwig Burger (1825-1884)

Age of Magic

Unexpected by the three Norns, who meddled with this world and would probably have wiped out the human race with their experiments... And unexpected by the three Fates, who came from a third parallel world with both technology and ethics, and who defeated the Norns at great loss to themselves...
... the Norns' technology of thinking machines lived on after they were no more.
It was a technology of microscopic nanobots which could evade notice of the natives with their lesser capabilities. They were programmed to watch for verbal and somatic commands from the more advanced race and hide from the technologically inferior race.
So what happens when this parallel world develops near equal technology? They become identical to the more advanced race which held the reigns of the nanobots. Then the nanobots start obeying the wishes of the locals.
And hilarity ensues.

Type

Consortium, Research