Darkmount was built in ancient times around the natural smelter known as the Upper Pool, to defend it from primitive creatures spun-off from the Transformers own creations. Below it lay the Lower Pool.
In the last days before the great war, Darkmount was basically a large inhabited ruin. The settlement of Polyhex spread out from its flank, separating the Upper Pool of magma from a series of high class upper-caste homes on the opposite cliff face. Below, a community of artisans made their homes around the edges of the Lower Pool.
Wheeljack participated in a battle there during the war. The Wreckers were caught between a Decepticon Patrol and the smelting pit. Wheeljack cleared them a path and used the bodies of dead Decepticons as stepping stones to escape via the smelting pool.
Bumblebee and his team visited Darkmount so they could look for clues as to the whereabouts of Shockwave. Unfortunately it was also the first place Unicron went when he arrived on Cybertron, and during the ensuing fight, the Autobots were almost knocked into a smelting pit. Starscream later returned there, believing he could take his place as Decepticon leader, but instead he encountered Predaking out for revenge.
Starscream survived by accidentally triggering the fortress' intruder defence system which killed Darksteel and Skylynx. He later found the laboratory where the Weaponizer Mini-Cons were kept before he decided to use them for his own benefit.