Eregion

a realm of the noldor elves in middle-earth, in eastern eriador, in the foothills of the misty mountains close to moria; also known as hollin. its capital was ost-in-edhil, which means “fortress of the elves”.

founded in the year 750 of the second age by galadriel and celeborn, eregion was later ruled by celebrimbor. it was visited by sauron in the fair form of ánnatar the gift-giver in the thirteenth century of the second age. it was here, circa s.a. 1500, that the rings of power were forged under sauron’s supervision, when the elven smiths were at the height of their power. in s.a. 1590, after the creation of the seven and the nine, celebrimbor secretly forged the three rings — nenya, narya, and vilya — for the elves. ten years later, sauron forged the one ring in mordor and completed construction of the barad-dûr.

it was at this time that celebrimbor perceived sauron’s intentions for the rings, and refused to give in to his request for them. thus, in s.a. 1693, the war of the elves and sauron began; two years later, sauron’s servitors invaded eregion. gil-galad, high king of the noldor, dispatched troops under the command of his lieutenant, elrond, to engage sauron’s troops; but by 1697 eregion, along with the rest of eriador, was overrun and celebrimbor killed. however, before his death celebrimbor managed to have the three rings concealed from sauron’s gaze and were never corrupted by him, though the seven and the nine fell into his hands: nenya, originally worn by celebrimbor, went to galadriel; narya went to gil-galad’s other lieutenant círdan but was later given to gandalf; and vilya was worn by gil-galad himself before it p-ssed to elrond at the former’s death.

many of the surviving noldor of eregion fled to lothlórien with galadriel, or to gil-galad’s realm in lindon, though some went north with elrond to found the hidden refuge of rivendell. even after saron was defeated in s.a. 1700 and driven out of eriador with the help of men from númenor, eregion was abandoned and remained empty even during the events of the lord of the rings trilogy.
the fellowship of the ring p-sses through eregion in the first book/movie on their way to moria. they p-ss by the ruins of ost-in-edhil, where legolas hears the stones of the ancient city whispering of its long-gone occupants:

“deep they delved us,
high they builded us,
fair they wrought us…
but they are gone.”