The Binding of the Last Dragon, in an age when the world was still young and magic flowed more freely, during a time of great upheaval and conflict among the ancient races.
Malnaar, the last of the ancient black dragons, had raged across the one great landmass of the world. He was finally captured by a coalition of dwarves, elves, and humans, and bound in the north, in what would become the Runebound Citadel. It was the only imprisonment he would ever know.
The chains were forged by the dwarven family Gul'durak, the Debt-Cutters (in Durûm: gul debt, dur cut, -ak those who do). Humans called them by their honorific, Fesselschmied, the chain-smiths, and the title became one of great honor among dwarves, symbolizing unmatched skill in metalwork and enchantment.
The Fesselschmied chains were imbued with runes that made them unbreakable except by someone of the smith's bloodline. The binding was cut as a gul-ûr, a debt sworn cut-eternal, and the debt was laid on the whole living bloodline: eight sealed name-columns, one for each Gul'durak heir. So long as a single Gul'durak lived and held the oath, the chains held. To free the dragon, someone would have to end the entire family in one stroke, before any heir could be born or sworn. For centuries that was thought impossible.
This placed immense responsibility on the descendants of the original smiths: to guard their secrets, to keep the line unbroken, and to ensure that Malnaar remained bound.
After roughly 1100 years, the Gul'durak were murdered: eight deaths in one night, the youngest last. The murderer broke not a single rune. With no living debtor, the binding did not release; it turned hungry, and the nearest thing for it to draw on was Malnaar himself. It fed him the stored debt of centuries. He broke free, and what followed was the end of the old world: see The Reawakening of Malnaar.
The Citadel still stands. Its chains hang empty, but the array is a sealed working with no debtor: in Durûm terms toth-hungry, still drawing on the north around it. What the world calls the weakening chains of the Citadel is that hungry working fraying.
The surviving treatise of one of the last Gul'durak (see Durûm, section 7.5) is the main dwarven source on the binding, but it is not reliable on every point. Its author claims the family never used chains ("chains are toth, dead iron") and that the Maelstrom opened "where the Citadel had stood." Both are wrong: the Fesselschmied chains are historical fact, and the Citadel still stands. Whether the author erred in grief, or wrote to protect the family's craft, is unknown.