The Anvil of the Void was a device used by the dwarves to create golems during the First Blight. It was forged by a dwarf of House Ortan named Caridin around -255 Ancient (940 TE). Caridin was made Paragon for his achievement. In -248 Ancient (947 TE), at the height of the battle against the darkspawn, Caridin vanished, and the Anvil of the Void's location was lost, seemingly forever.
The Anvil was the key to forging golems. However, Caridin knew he could not make a living creature out of non-living materials. He realized that to create a golem, a life had to be taken from elsewhere to power it.King Valtor, the king of Orzammar at the time, began having prisoners and his political enemies forcibly turned into golems. Finally, it became too much, and Caridin refused to cooperate. He was transformed into a steel golem for his defiance. However, his apprentices lacked the skill to forge a control rod to manipulate him, and Caridin retained his free will. He sealed the Anvil away in the Deep Roads, beyond the reach of Orzammar.
The Warden can destroy the Anvil or retrieve it (which is available only by siding with Branka) and use the new golems to protect Orzammar and also use them against the Fifth Blight as part of the quest A Paragon of Her Kind.
Upon the Anvil, a crown will also be forged by either Caridin or Branka for the new king of Orzammar. It will be created very quickly given its number of details possibly due to the magical abilities of the Anvil. If the Anvil was destroyed then news of it's discovery quickly spreads, and taking advantage of the reduced Darkspawn population a few determined smiths found and rebuilt the anvil and created a new Golem using a Spirit of the Fade.Which apparently immediately went insane and killed several people before it was destroyed leading to a complete barring of Golem research, although a few still advocate Caridin's research.