Look up anywhere in Arc and you'll see it: a wide purple band across the sky, full of dark rocks that drift, huge and silent. They never fall. Nobody knows why.
People call it the Rift. It's there over the market in the morning and over the fields at night, glowing softly when the sun goes down. From high enough, they say, you would see it go all the way around the world: a ring, with Arc in the middle.
Children point at it. Old people don't. It has always been there. Grandparents say it was there when they were small, and their grandparents said the same.