On the surface there is little to see: a beam a shade darker than its neighbours, faintly cracked across the grain into small cubes, as if it had been charred without fire. Where the rot is open it shows as a flat, wrinkled skin the colour of rust or old leather, edged with white, spreading over wood and on across the stone beside it, and in still air it throws a fine brown dust of spores that settles on everything below. Grey strands as thick as a bootlace run from it through mortar and over brick to find the next timber. It smells of mushrooms and damp earth, strongest when a cellar door is first opened.

It wants timber, still air, and a damp that is never wet: cellars under ruined storeworks, sealed rooms, the backs of old culverts, and the wooden bracing of collapsed works. It is commonest in the oldest and least aired underlayers of the Marches and in the storework cellars under Lowbank.

The rot spreads slowly and out of sight, through the heart of a beam before it shows at the skin, and it crosses stone and brick by its strands to reach dry wood far from where it began. Opening a cellar to the air checks it; closing one again lets it run.

It takes the strength out of wood while leaving its shape: a rotted beam keeps its look and its colour until a load or a knock crumbles it to brown powder. It reaches timber across masonry no other rot can cross.

It gives nothing but warning work. Salvage crews test every old beam with an awl before they trust it, and the Kindred danger-marks on the stones grade a rotted cellar with the unbraced. A rotted prop can bring a cellar roof down on whoever stands under it, and rot carried in on salvaged timber spreads into the new beams of the building that bought it. The spore dust gives some cellar workers a cough.

In the Marches "sound-looking" is a warning word, said of timber and of promises alike. Goblin households say the rot follows a building that nobody remembers, and that a cellar used and talked about keeps it off; the airing that comes with use does the work. Kobold crews, who brace by sound, say a rotted beam rings wrong under a tap, and they are right.

Salvage crews tell of the cellar under a fallen manor that held a lord’s buried strongbox and a rotten beam over it; the crew that dug it out is under the beam still, and the strongbox with them.