Moat Cailin

Ruined guard of the Neck

Three crumbling towers commanding the causeway through the swamps of the Neck — the ancient lock on the door to the North.

The fuller tale

Moat Cailin is the lock on the North’s only door. Where the causeway threads the swamps of the Neck, the First Men raised a fortress of twenty towers on the one patch of solid ground — and though ten thousand years have reduced it to three leaning ruins, the ground still does the work. Any army marching up from the south must come single file along the causeway, under bowshot from the towers, with bog on both sides and the crannogmen poisoning the flanks. The maesters count the southern kings who tried to force it; the swamp keeps the actual tally.

The catch, known to every northern commander, is that Moat Cailin only faces one way. Taken from the north it is nearly worthless — which is why the ironborn seizing it lands like a knife between the shoulders: Balon’s raiders take the towers from behind and bar the door with the North’s own lock, stranding Robb’s host on the wrong side of his kingdom. The garrison rots there for years until Ramsay Bolton retakes the ruin in his own fashion — a surrender negotiated by a broken man in a dead man’s persona, honored precisely as long as it takes to flay the survivors.

In the tale’s architecture the Moat is the North’s thesis stated in stone: this country cannot be conquered, only betrayed. Every disaster that befalls the North in the war comes through a door someone opened from inside — and the great ruined lock on the causeway stands there throughout, undefeated and irrelevant, waiting for a war that respects geography.

The chronicle here

Catelyn meets Robb's host at Moat Cailin and does not send him home to Winterfell — she teaches him how to spend his one throw of the dice. (AGOT 56)
Reek rides to Moat Cailin under a peace banner to talk the ironmen out of an unwinnable ruin; Ramsay flays the garrison anyway, and Lord Bolton comes home to the North. (ADWD 21)