Imperial Crest

I really need to get to work tomorrow, but had to finish the 2nd icon in my WH 40k series: the Imperial Initiative.

Trivia: The ultimate leader of the imperium is forever imprisoned on what?

Prize: Free copy of the Macish png icon set: http://eddit.com/shop/macish_icon_set/

First comment with the right answer wins. Heading out for the day but will check back later tonight for the winner.