|Location||At the confluence of Sirannon and Glanduin|
|Inhabitants||Elves of Eregion|
|Etymology||S. "Fortress of the Elves" |
(ost "fortress" + edhil "elves")
|Events||Sack of Eregion|
- "Deep they delved us, high they builded us, fair they wrought us, but they are gone."
- ― 
Ost-in-Edhil was founded by Galadriel and Celeborn, before the time they ruled Lothlórien. The Elves began trading with the Dwarves of Khazad-dûm and built a large road to connect the city with the West-gate of the Dwarven kingdom. The Elves of Eregion also traded with the Men of Númenor. After the Númenóreans founded the city of Tharbad to the south of Ost-in-Edhil, Galadriel is recorded meeting with Aldarion before he took up the Sceptre.
In time the Gwaith-i-Mírdain, a brotherhood of Elven craftsmen, was founded. They were led by Celebrimbor, the greatest smith since Fëanor. Sometime after [[Second Age 1350| SA 1350}} Galadriel left for Lórien and Celebrimbor became Lord of Ost-in-Edhil.
In 1200 a mysterious craftsman named Annatar came to the city, offering his considerable talents. For 400 years they learned from him and together forged many Rings of Power. Annatar was, in truth, Sauron, who returned to Mordor to forge the One Ring. The Dark Lord returned with an army of Orcs and began the War of the Elves and Sauron, in which Celebrimbor was slain and Ost-in-Edhil was completely destroyed.