The Emperor's Amphitheater was a large room chamber located on the planet Qo'noS in the Emperor of the Klingon Empire's official residence. It was stated to be the largest room present on the Klingon homeworld where only the Emperor was permitted to speak from that place.
In 2376, Morjod, son of Martok conducted a coup in the Klingon Empire in order to make himself the head of the Klingon High Council. After taking control from his biological father Martok, son of Urthog, Morjod made a public speech from the Emperor's Amphitheater which was previously the location where Emperor Kahless, son of Kahless was permitted to speak with the people. (DS9 - The Left Hand of Destiny novel: Book One)