ok so. in HtN, harrowhark is wandering around the mithraeum and there’s this wall of arches and bones with rapiers, and she keeps being drawn back to the black one. anyway, I’m transcribing the quote from the audiobook, so pls forgive any punctuation/formatting inaccuracies:

“there were 9 decorative arches on the eastmost side of the room. you had by now investigated each arch carefully. the brown floor tiles were inlaid halfway up the wall in these arches and then became glass of every different color. and in the center of each polychromatic sweep was a sword bracket. some of the brackets were empty, and some held rapiers. one in particular always drew you back to it. a black rapier with a basket hilt formed of ebon wires. at the termination of each wire was a single canine tooth, and the end -pomel - was a soft warm knob of black dyed bone”

(HtN, ch 16)

and i am CONVINCED that

1) the arches represent the original lyctor/cav pairs and john. the rainbow aesthetic for the lyctors (combination of colors, before they split into seperate houses, plus it matches the rainbowy cloaks they all wear), 9 of them, etc

2) that is the sword of Samael Novenary. black! bone pomel! teeth in the basket hilt! (and this could be reaching but. Anastasia and Samael were alone with John when he killed Samael. Samael’s rapier might well have been the only killing weapon in the room…. though Jod being God, maybe he didn’t need a weapon but what i’m saying is… murder weapon. grave goods. revenant?)

3) in addition to the black rapier described belonged to Samael, and I think the other rapiers in the brackets are the recovered weapons of the cavalier’s/lyctors who have died. or symbolic representations of them. the text never mentions specifically how many, and which, brackets are empty vs which ones/how many have a sword in them, but i’d wager the only empty brackets would be the second, fifth, and eighth (because they are all actively using their swords).