Altar of the Emeralds

The Altar of the Emeralds is a location that appears in the anime series Sonic X and its comic series published by Archie Comics. It is a large and ancient shrine on Angel Island that the Chaos Emeralds and Master Emerald have been stored in at various points in history.

Description
During the Knuckles Clan's reign, the altar was surrounded by a giant wall built upon large pillars. The inner sanctuary consisted of seven pillars, each which had a Chaos Emerald pierced on top of it. The central shrine hosts a low-set pedestal for the Master Emerald to rest on which acted like a fountain from where water poured from. After the Perfect Chaos incident, the Altar of the Emeralds was heavily damaged. In the present day, it shows a ruined exterior wall and central shrine, and several pillars are either missing or destroyed. All its water has also disappeared.

Past
Generations ago, the Altar of the Emeralds was once a part of the Mystic Ruins on Sonic's homeworld, where the Chaos Emerald and the Master Emerald resided. Back then, it was inhabited by the Chao and their guardian Chaos.

During the reign of Pachacamac, the Knuckles Clan tried to steal the Emeralds from the altar to empower themselves. Tikal tried to make Chaos leave the altar with the Chao, but it declined. Similarly, Pachacamac refused to not take the Emeralds for his own gain, and thus injured Tikal and the local Chao when they tried to stop the clan's raid of the altar. Fueled by anger, Chaos used the Chaos Emeralds in the altar to transform into Perfect Chaos and nearly erased the Knuckles Clan from existence. To save the rest of the world from Chaos' wrath, Tikal sealed herself in the Master Emerald along with Chaos. From that point on, the altar was left broken and stayed on what would later become Angel Island.

Chaos Emerald Saga
After acquiring the red Chaos Emerald, Knuckles had a vision of the Master Emerald and the Altar of the Emeralds from the distant past.

Chaos Saga
Six months after Angel Island was brought to Earth by Chaos Control, Dr. Eggman attacked the altar and released Chaos (as well as Tikal), leaving the Master Emerald shattered and its shards scattered far and wide. Knuckles thus made several trips to the Altar of the Emeralds during his quest to restore the Master Emerald.

Shadow Saga
Seeking an emerald to earn Dr. Eggman trust with for a mission, Rouge the Bat visited the Altar of the Emeralds and stole the Master Emerald. A spitting-image of the Altar of the Emeralds was soon after discovered inside the Eclipse Cannon which was used to channel the power of the Chaos Emeralds into the Space Colony ARK. To stop the ARK from colliding with the Earth, Sonic and co. put the Master Emerald into the artificial altar to nullify the Chaos Emeralds' power.

Homebound Saga
When it was discovered that the presence from everything from Sonic's world would cause time to freeze on Earth, the Altar of the Emeralds was warped back to Sonic's home world, along with Angel Island.

Metarex Saga
When Chris' parents tried to send their son's belongings with him to Sonic's home world, they were sent to the Altar of the Emeralds using Chris' teleporter, along with a spaceship for the Chaotix to take them to him in.

By the end of their battles with the Metarex, Knuckles brought the Master Emerald's shards to the altar where they could heal naturally from using up all their power to help defeat the Metarex.

Trivia

 * During the episodes in the first season of Sonic X that showed the Altar of the Emeralds, the altar is missing some of the pillars that was shown in the third season.