In the year 750 of the Second Age, many Elves of the Noldor left Lindon and went into Eriador.

There, near the west door of Khazad-dûm in the White Mountains, they founded the realm of Eregion and built the city of Ost-in-Edhil, the "City of Elves".

These people who lived there were the Gwaith-i-Mirdain, the Elvensmiths who in the year 1500 forged the Rings of Power.

Ost-in-Edhil was a fair and prosperous city with its white elven towers rising up in the midst of the holly forest of Eregion.

In the War of the Elves and Sauron, in SA 1697, Ost-in-Edhil was utterly destroyed and the realm of the Elvensmiths was no more.
Encyclopedia entry originally written by Gil_Estel101