From Teletraan I: The Transformers Wiki

The Council Citadel is a structure in the Beast Machines portion of the Generation 1 continuity family.

Standing above its surroundings in the capital city of Cybertron, the Council Citadel served as the meeting place for the Maximal Elders.

[edit] Fiction

[edit] Beast Machines

After "purifying" Cybertron, Megatron made it his base of operations, turning the meeting room into his throne room (although he was technically part of the ceiling). Master of the House

It was also where he originally kept the sparks of the kidnapped Transformers. Fires of the Past

During the Vehicons assault on the big floating head, it crashed into the Citadel after losing all its power, but without damaging the Citadel itself. Somethings are built to last. Endgame Part 1: The Downward Spiral