The Gwaith-i-Mírdain was a brotherhood formed by Celebrimbor and the other master craftsmen of Eregion in the Second Age and their capital was Ost-in-Edhil. They stood close to the Dwarves of Khazad-dûm and their mithril mines. They cooperated for about a thousand years, and their rare friendship was the closest between Elves and Dwarves in history. Celebrimbor helped to construct the famous and magical West-gate of Moria. They were said to be the most talented artisans to have worked since the time of Fëanor himself (who was Celebrimbor's grandfather).
Sauron after failing with Gil-galad and Elrond, targeted the Gwaith. In the guise of Annatar the "Lord of Gifts" in S.A. 1200 he presented himself as an agent of the Valar and taught them how to forge the Rings of Power. The Gwaith were easily tempted since they wanted to bring to Middle-earth the joys of Valinor. The Rings would prevent or slow the decay of the mortal world, preserve what is desired or loved and also enhance the natural powers of a possessor even if that would mean disrupting the natural course of the mortal world.
The Gwaith together with "Annatar" made several rings in S.A. 1500. Celebrimbor presented King Durin III with a Ring of Power. When Annatar had left (actually for Mordor) about S.A. 1590 Celebrimbor made the Three Rings partly using the teachings of "Annatar".
Then Sauron betrayed them and forged the One Ring. However the Gwaith realized his plan and denied to hand him their Rings, resulting in the War of the Elves and Sauron. Eregion was devastated and the survivors of the Gwaith retreated to Rivendell
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