Sci-Fi novel about a world with early iron age technology, it is a world shaped like a flat disc on a giant pillar

Question

I read a Sci-Fi novel a few years ago, it concerns a world with early iron-age technology that is a giant disc supported on an immense pillar. A cyborg is sent to study the people and report back to someone about them. They called the disc "the drum" as it made a certain sound when horses ran on the ground. They had primitive guns and rode horses instead of having vehicles. It was an artificial world, but it is not said who created it. There are mountains ringing the edge and one of the people accompanies the humanoid Cyborg to the edge to see it. Then he leaves.

There were no sequels, it was just one book.

Answer 1

This is Otherwise: Three Novels by John Crowley, specifically the novelette The Deep.

In a twilight land, two warring powers -- the Reds and the Blacks -- play out an ancient game of murder and betrayal. Then a Visitor from beyond the sky arrives to play a part in this dark and bloody pageant. From the moment he is found by two women who tend to the dead in the wake of battles, it is clear that the great game is to change at last.

The text mentions that the world (The titular 'Deep') is also referred to as 'The Drum'. Our protagonist is some kind of sexless android.

The world is founded on a pillar which is founded on the Deep. Of the world, it is a great circle; its center is the lake island called the Hub and its margins are waste and desolate. Of the pillar, it is of adamant. Its width is nearly the width of the world, and no man knows its length for it is founded on the Deep. The pillar supports the world like the arm and hand of an infinite Servant holding a platter up.”

and...

"The great gray heath they walked on was called the Drumskin. Their footsteps made no sound on it, but when the herds of horses pastured there rode hard, the air filled with a long hum like some distant thunder, a hum that could be heard Inward all the way to the gentle folded farmland called the Downs, all the way Outward to the bleak stone piles along the Drumsedge, outposts like Old Watcher that they could see when the road reached the top of a rise, a dim scar on the flat horizon far away."