The other books of this series are about peoples: what they are as kinds, and what they make of an era. This one is about everything else that lives, grows, walks, or lingers in Caeldon and the planes behind it. It began as a set of working pages, one to each being, written to keep the world’s herds, crops, and monsters as consistent as its rivers and its roads, and it became a book when it was clear that a writer wants them as much as a scholar does: a crop for a field, a beast for a road, something in the fog that should not be followed.

The book is compiled from those pages. Its first chapter, The Living World, and the short openings of its shelves were written for it; its entries were not. Each entry is its canon page, gathered into the book as it stands, so that the book and the pages can never drift apart. When a page is corrected, the next edition of the book carries the correction.

It stands beside the rest of the series rather than after it. Foundations explains the planes, zones, powers, and magic that so many of these beings belong to; the era books describe the peoples who herd, hunt, fear, and pray about them. The entries describe each being as it lives in the Medieval Era, the one era the series has told so far. The website’s Reference at joetjen.github.io/The-Decachord/ has every entry too, with the rest of the setting around it.

A bestiary is an old kind of book, and the old ones were full of what people believed. This one keeps belief as well, but it keeps it apart: what a being is and does stands in its entry plainly, and what the peoples say of it stands beside that, under its own heading, for the reader to weigh.