At the same time, Orcs once again became "well-armed and very numerous, cruel, savage, and reckless in assault. In the battles that followed the Dwarves were outnumbered, and though they were the most redoubtable warriors of all the Speaking Peoples they were glad to make alliance with Men."[3] The Orcs were all the more easily defeated by the new combination of Khazad-dûm's heavy infantry and the horsed archers provided by Men, and the Longbeards consequently came to dominate the northern and central Hithaeglir and the lands east of there, although Khazad-dûm had always "regarded the Iron Hills, The Ered Mithrin, and the east dales of the Misty Mountains as their own land".[3] Ultimately, these Men then assisted the dwarves of Khazad-dûm "in the ordering of the lands that they had secured".[3]
With the foundation of the Noldorin realm Eregion to the west of Khazad-dûm around the year 700,[7] friendly relations between the Longbeards and the Elves became firmly established. Many of the Elves then became involved in the development of Khazad-dûm's mansions as a consequence, and it "became far more beautiful"[7] during this period. This friendship also resulted in a massive subterranean extension westwards: the Dwarrowdelf's habitable parts remained in the eastward side, but passages were delved through miles of rock that terminated at a gigantic stone portal outside this elven realm — The West Gate — "which opened out into their country and was chiefly used by them."[3] Celebrimbor, the Lord of Eregion, used mithril lettering on the dwarf Narvi's behalf when the latter built these, to create an inscription that read Im Narvi hain echant. Celebrimbor o Eregion teithant i thiw hin: "I, Narvi, made them. Celebrimbor of Eregion drew these signs."