Port Cecil
"Rumpled convolutions of coral fill the water, glimmering with silvery light. The harder you look, the more you see shapes amid the chaos, almost as if they were sculpted. This one could be a crenellated castle: that one, a horse's head."[1]
The Principles of Coral is a massive coral reef in the Unterzee. Its primary port is Port Cecil.
A Dying Reef...
"Beneath the beckoning light of the Impostor Moon, the shining body of the Principles of Coral is being chased beyond the waterline. The old peace of Port Cecil has been transformed by the push and pull of tide and industry."[2]
"Used to be the reef itself would rise up against thieves, but the Principles ain't wot they were. ... Happened all at once. One day, someone breaks off some coral without gettin' their eyes all burned out. The next, London's maw opens on our doorstep."[3]
The Principles of Coral are abuzz with industry today, though it was not always this way. Until recently, there was only a small Rubbery population at Port Cecil,[4] and a similarly small community of coral-encrusted humans;[5] other factions from around the Neath gathered here to play chess and hold diplomatic meetings.[6] The past several years have seen a further wave of settlement across the Principles,[7] as Iron & Misery Company has begun mining its coral, and has built refineries to extract valuable scintillack.[5]
The reef is lit by the mysterious Impostor Moon, which is seemingly a sentient creature.[7]

The island's remaining native fauna include lamp-cats, foraging felines with gills and glowing lures on their heads. They are emissaries of the Light-in-Exile, the giant anglerfish that dwells under the Magistracy of the Evenlode,[2] and they work alongside the Rubbery locals to stop the miners and preserve the reef.

...And a Dying Art
"A sourceless silver glow. A haven for players of games."[8]
Once upon a time, the Principles was bathed in a dreamlike soft silver light. Its few inhabitants were strangely fond of chess, playing obsessively as if under a hypnotic spell. They used chessmen made of scintillack, a kind of glowing coral found all over the reef, and watched as their pieces seemed to enact their own individual agendas. Their games mirrored the power struggles of the Neath, between the Lorn-Flukes, the Echo Bazaar, Mt Nomad, the zee-gods, the Fathomking, the Khanate, the Surface.[9][10] For the reef was the true center of the Great Game, and it still is yet.[11]
Chess is now a rare art in the reef, though the Disillusioned Grandmaster stubbornly hangs onto her club, the Poisoned Pawn.[11]
The Principles of Coral
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"Between stars. Descend the chain. I rest here. I forget."[12]
"The game soothes the pangs of dissolution in. But I want so to be less. I am tired of thought. Will you help me? Sleep will not enough. I desire no dreams. Will you help?"[13]
The Principles of Coral, also called the Shining Mind,[14] is actually a formerly sentient, chess-loving power,[13] waited on by Rubbery Men.[15] The Mind was the true source of the silver glow that once lit Port Cecil from beneath,[16] and it would rarely speak, almost telepathically, to certain visitors that drew its attention.
The scintillack pebbles that dot Port Cecil are broken bits of the Principles of Coral, and they are as alive as their host, with none of the experience or weariness that currently troubles the Principles.[12] This scintillack is also used to mark the servants of the Principles, burning them with distinctive, glowing scars.[17][18]
The Principles of Coral was once a Lorn-Fluke,[17] but it grew exhausted as time went on. To free itself of its sentience, it strove to descend a few rungs down the Great Chain of Being,[19] and by the 1890s it was already much of the way there; hence why it appears inanimate, but is still very much alive.[17] To continue its descent, the Principles of Coral had to lose a chess game, with the Nacreous Outcast serving as its surrogate;[20] it also had to provide a second creature, acting as a "counterweight" of sorts, with an ascension, thus satisfying the Chain's arcane rules and sending the Principles into the dreamless sleep it so sought.[19][13]
Perhaps most importantly, the Shining Mind never, ever felt regret. Not even when it left Axile with its fellows on the behest of the Bazaar; not then, and certainly not as it willingly sank into oblivion.[21][22]
Scintillack Chess
"You don't often look at chess-pieces: not really look. The Bishops, with their hooks. The Night, with its mane and teeth. The Kin and the Cream, white mingled with red. The Roots that pin the corner of the board down, to keep you safe from your opponent. You lift a Paw to toy with it: touch its velvety pads."[9]
"Checkmate. Look too closely, did we? You need to be careful with scintillack chess-sets."[9]

The strange chess played in the Principles is quite dissimilar to the chess familiar to those from London. The scintillack chess pieces seem to take on slightly different, but still recognizable, forms,[9] and this strange game isn't localized strictly to the reef; it may also be played by very specific agents of the Great Game.[23] However, these pieces need not strictly be scintillack; they may be made of other materials, perhaps for the sake of symbolism or practicality.[24]
- Nights are said to have manes and sharp fangs, and may wound those who move them.[9][25] The Principles considers them ornamental, but such ornaments are, after all, vital in chess.[26]
- Bishops appear to take on a spiraling shape and possess sharp hooks.[27][9] The Principles of Coral uses its Bishop as a counterweight for its descension on the Great Chain of Being.
- Roots are the corner pieces of the chessboard,[27] and serve as protection from a player's opponent.[9] The Principles uses its own Roots to protect against its troublesome, but incurable, fear of its own impending descent.[28]
- Paws are considered relatively safe pieces to move,[29] and the Principles seems to use Paws to represent the works of its servants, such as the Rubbery Men.[30]
- Pawns are mentioned, but their purpose is unknown, and it's unclear whether these pieces are separate from the similarly-named Paws.[23]
- The Cream is described as a "terrible" piece; this presumably indicates it possesses great power on the chessboard.[27]
- The Kin is the most important of the chess pieces, and its victory or defeat can determine the outcome of a chess match.[20] The Principles of Coral seems to use its Kin to represent its family, the Flukes, and perhaps as a representation of what it once was.[17]