The Marches
The world Greywater is fought in. The full World Bible is a free download; this is the short version.
Where it is
The Marches are a strip of walled towns about three hundred miles long and eighty deep, a fortnight on foot from end to end if the road's dry. They used to be the eastern border of a kingdom called Ossary. Ossary's gone. The Marches are the bit that was left standing, still guarding a border with nothing on the other side of it but the dead.
Seven walled towns and the farmland between them, strung along the Marshal's Road: Greyfold, Cantmoor, Harrowgate, Vellbridge, Stillwater, Thornhallow and Marrow. Harrowgate is the biggest and the Chapter of Towns sits there. Marrow is the furthest south and the poorest, and it's been burned to the ground four times.
It rains. Buildings are stone at the bottom and timber at the top, steep roofs, black beams. The State Army doesn't shine: blackened plate, wool in dull town colours, banners that are usually wet. The dead aren't bone white either; they're the colour of the moor.
The Dismissal
Everything is dated from one day. Three hundred and eleven years ago Ossary appointed a Grand Marshal to fight a war on the eastern border, and when the war was won the Royal Council dismissed him, the way it always had. He said no. His name was Casimir Drauve. He hanged the courier from the gate of Harrowgate, marched on the capital, took it, and ran the kingdom for eleven years as Lord Protector until it fell apart in his hands. Then he went east into the Barrowfield to ask the old kings for help. The thing that commands the dead on the Greywater wears his armour.
The Marches exist to make sure there's never another Drauve. A Marshal is appointed for one campaign and goes home after it. The army belongs to the towns, not to him. It's a slow, suspicious, expensive way to fight a war, and they've never lost a town for more than a season.
The Undertow
Magic comes from a current under the world. The Flow is the living current: weather, fire, growing things. The Colleges teach it in five schools, the Five Lamps. The Ebb is the current going the other way, out of the world, strongest where things have died. Every necromancer the Marches have ever faced learned it in a locked College room. The Ebb pulls back, and what it pulls on is the wizard.
The dead
The dead don't get up on their own; something has to draw them. They remember: a skeleton that was a soldier stands in a line. They don't tire, don't run and don't stop when they fall. Sunlight slows them. Iron bothers them. Vampires aren't risen dead; they're living people who went into the Ebb on purpose and came back with it inside them.
The Caithe
North-west of the Marches, up where the Sallow starts, is a country that was never Ossary's: lochs and glens, black water and bare hill, running north and west till it hits the sea at the Skerries. Clan country. No king, no road, no town, and the old world still alive in it. The Marches have the dead. The Caithe has everything else: the kelpie, the selkie, the wulver, the Cu Sith, the trolls and giants and dragons, and the Ghost Piper of Dunmorran, who plays on the battlement at dusk for every Caithe man who died away from the hills.
The Drowned Coast
East of the Barrowfield the land drops to a coast of black cliffs and wrecks that nobody has mapped. The Ebb runs in salt water as well as earth, and what it pulls up out of a drowned ship is the Drowned: every crew the sea took in a thousand years, bound together, coming ashore in storms ahead of something worse. They answer to no necromancer. They answer to a ship's bell.
The Iron Fells
Under the mountains north of Greyfold live the Stonewrought, who have traded iron for grain down the Caulder road for nine hundred years without anyone ever seeing one. Something has started digging up into their halls from underneath, and for the first time anyone can remember, messages have come down the mountain with the iron. The last one said: we are coming down.
How far it is
Harrowgate to Greyfold, 130 miles. To Marrow, 140. Across the Greywater to Ashgrave, 80, which is five nights for the Host and why the walls always know it's coming. To the Harrow Pass and the Caithe, 115. To Aulderne, the empty capital of Ossary, 300. To the Drowned Coast, 300, and nobody's walked it in daylight since Drauve. The known world is about fifteen hundred miles across, and most of it is nobody's.