LAST EDITED ON Aug-01-01 AT 02:26 PM (EDT)

Alright, lemme try my hand here... I'm not going to be entirely accurate, as I have a bad habit of not keeping the info in my brain current, but this ought to clear things up a bit.

First of all, a Dyson Sphere is a huge, ridiculously huge, really damn big hollow sphere, which one could conceivably construct around an entire star, perhaps an entire solar system, thusly enabling one to harness almost the entire sum of energy said star radiates. This energy can be used for a variety of purposes, not the least of which are climate control and terraforming of planets inside the sphere.
If I recall correctly, New Avalon is a rather large city that was built on the inside surface of the sphere. As such, it can and probably does stretch to the horizon, but if one took the time to circumnavigate the vast circumference of the sphere, one could eventually return there. I suppose it would make for an imposing military blockade, a spherical, cosmic scale Maginot Line, and the chances of its destruction are lowered by its sheer size. However, if it were destroyed, the results would be catastrophic to the point of making Sonset look like a cheap firecracker.
I leave the socio-politikal (sic) questions, and the correction of my errors, to Those Who Know (tm) ^_^

TRB

"I wish I was reaper, culling lost souls. I wish I could cast them into deep and lonely holes."