While there are certainly realms powerful enough to lay seige to and
conquer the Imperial City, there many other factors that may keep
regents from doing so. First, most regents see the approval of the
Chamberlain as central to being proclaimed emperor...and with him
removed, that would obviously be impossible. Becoming Emperor would not
be so easy--conquering a whole new empire would take a long time. Any
regent who attempted to attack the city would face the wrath of all the
other regents, and no regent could long survive that. Second, perhaps
there is a cultural regard towards the city. During the days of the
Roman Republic it was unthinkable (illegal, in fact) for a Roman General
to march troops into the City. Although there are many differences
(Anuire is not a unified nation, of course), perhaps there is still a
cultural taboo against marching against the City. And for the 500 years
since the fall, no one has dared to cross that line. But, all it takes
is one regent to decide otherwise, as Julius Caesar did, and the City
will be under seige. Would Gavin Tael try it if he were close enough?
He might. Diemed or Avanil? I don't think so. In fact, they probably
see themselves as protectors of the city, guardians of the glory of the
Empire. But, maybe their successors will not see it that way...

Brian