The Antikythera Mechanism
Have you ever heard of the Antikythera Mechanism?
(a modern re-creation of the machine)
This was a clockwork computer which was recovered from an ancient shipwreck off the coast of Greece back in the year 1990. The device is simply amazing in a number of different ways; it seems to have been built some time around the year 100 BCE, and employs the sort of technology which the world would not see again until the 18th century; a complexity and miniaturization of gears that was literally MILLENNIA ahead of its time. What's more, it seems to have been built to keep track of the movements of the earth, moon, sun, stars and planets, presumably in aid of nautical navigation. Whoever designed this beauty seems to have had a solid grasp of the fact that the Earth revolved around the sun, rather then vice versa. In this, too, this inventer was thousands of years ahead of the rest of the world.
Imagine the mind behind this feat. The ancient world contains virtually nothing resembling this. There were other devices which employed gears and even a certain degree of clockwork, so it's not entirely unprecedented, but to sit down and take principles like this and construct a functioning computer capable of working out precise positions and calculations like this in a world where there was simply nothing else of its kind that had ever been conceived... and then subsequently vanished again, not to be seen again for nearly two thousand years? Imagine the loneliness and isolation of an intellect like that in the ancient world. Imagine being able to produce such notions with such primitive tools and resources to draw upon. Who knows what such a mind would be capable of with the technology and accumulated knowledge we have today.
And we don't even know their name. There is some suggestion that this may have been the device mentioned in an account by Cicero, in which he spoke of an instrument "recently constructed by our friend Posidonius, which at each revolution reproduces the same motions of the sun, the moon and the five planets." Certainly, it's difficult to imagine that there could have been two such men at one time in history while all around them they were surrounded by savagery and ignorance, but who knows?
It's at one time depressing to think of society possessing even one person capable of producing a work of genius like this and then utterly losing it, losing even the memory of it for countless centuries, rather than building upon it... and also tantalizing to speculate as to what might have been, if the tradition of this sort of invention had persisted instead of vanishing utterly. I'm frankly shocked that there doesn't seem to be any historical fiction, or indeed ALTERNATE historical fiction based upon this.