The seat of an empire (7)
I believe the answer is:
ottoman
This clue is a double definition.
'the seat' is the first definition.
(ottoman is a kind of seat)
'an empire' is the second definition.
(I've seen this before)
'of' is the link.
(Other definitions for ottoman that I've seen before include "Type of seat; Turkish" , "Couch for a Turk" , "Upholstered footstool" , "item of furniture" , "Turk (historical); seat" .)