Coliseum

The Coliseum was the main structure on Metru Nui, located in the center of the city. It was where Turaga Dume's resided, and the location where sports were played. During the fall of Metru Nui, Teridax used its vast basement to store the Matoran in his plan to take control of the Matoran.

History
The Coliseum had a long story, and it is unknown who built it and for what purpose. But whatever the case, the Turaga called Dume has always used it as his residence and place to govern the city from. In the Toa/Dark Hunter War, the Toa used it as their HQ, sending the Toa on missions from there. After the Toa won the war, sporting events resumed.

During the rise of the Makuta of Metru Nui, he used it to store the Matoran in its basement. The Toa Metru saved six, but vowed to return and rescue the others. During their absence, Sidorak and Roodaka took over the Coliseum and made it the Visorak base (under the orders of the Makuta). The Toa Hordika, aided by the Rahaga, saved the Matoran and defeated the Visorak hordes. This Toa victory was known as the Final Battle for Metru Nui. The battle of Metru Nui was the battle where Sidorak was killed by Keetongu.

The Toa and Matoran left the city for Mata Nui, but when it was rebuilt, they came back.

Important Features

 * The Sea of Protodermis
 * The gigantic basement, that was used to store the Matoran Spheres during the Great Cataclysm.
 * The balcony on which Dume, the Rahaga and Keetongu resided when they were rebuilding Metru Nui.

Trivia

 * After Matoro sacrificed himself for Mata Nui, a ceremony for him in which every Matoran joined was held in the Coliseum.