In the times before the coming of the current gods, a group of priests of the Ancient Ones built an altar.  The altar was dedicated to many of the Elder Gods, with a gemstone designating each one of the gods.  Of course this means that the crudely carved marble altar is liberally studded with gemstones.  The altar weighs about half a ton.  It disappeared soon after it was crafted, probably because of the Elder Gods’ loss of power.  It reappeared centuries later under the control of the aldar during a battle with the elves.  The elves captured the altar and secured it in an underground vault.  Years later when the elves decided to attempt to master the altar, it had disappeared.  Rumors alternately put the altar in the hands of the aldar or the tezinium.  There is no record of what power the altar has, but it is believed to channel the powers of the Elder Gods and possibly summon them or their minions.