We do not know what it is. We have never known what it is. What we know is only what it does — and even that knowledge has grown difficult to hold.
It does not arrive. It does not announce. A settlement that existed in the morning records still exists in the evening records, but the expedition that set out to reach it returns having found nothing. Not ruins. Not ash. Nothing. The land where the settlement should stand is unmarked, undisturbed, as though it never hosted anything at all.
The word for this process in the early Scholarium records is silencing. Later scholars preferred removal. The Choir of Glass used a term that does not translate into any common tongue — a word meaning, approximately, the forgetting that forgets it has forgotten.
The Quiet does not destroy. It erases. And reality closes over the erasure as cleanly as water closes over a stone.
Marginal notation, hand unknown:
By the time you notice it has taken something, it has already taken three more things you haven't noticed yet.