Cities in Orbit
Long ago, when the Dark Millenium was beginning, many wise men began to despair of combatting the forces of darkness and instead to consider flight. But if all Arth was to be a battleground, where could they flee to? Some fled to the cities of Lune, but in general, neither the Lunites, nor the rulers of cities on the other worlds were much inclined to welcome refugees. Indeed, most barred the entrance of strangers to prevent contamination by the forces at war on Arth, which did, indeed, lead to the fall of many of the cities of Soulcis, the second world. This policy of isolation eventually led to the forgetting of other worlds by the Men of Arth.
But some men of power were unwilling to abandon altogether the sites of their lives and triumphs, or the people dependent on them and were still unwilling to compromise with the Lords of Darkness. These mighty sorcerors banded together and contrived to take with them their castles, palaces and even whole cities, off the surface of Arth. Some fled into other dimensions, but most flew into the void between the worlds, perhaps intending to return at some later date.
The Dark Millenium lasted far longer than many had forseen, and it changed the surface of Arth forever. The flying cities were all but forgotten, and few ever returned. Some may have fallen prey to the forces of darkness, others foundered in the perils of the eternal void and others may simply wandered forever out of the ken of men. If ever the number of the flying cities was known, no man has the count of them now. Of those that still exist at all, the greatest part must be desolate, untenanted (at least by humans) - empty monuments to fallen magery. But some survive, testaments to the power of the magi who created and maintained them. Ages have passed and the inhabitants of these few survivors have no memory of the Arth of their ancestors. Self-contained worlds are all they have ever known. Even if the skycities could return to Arth, few living on them would wish it, or could even comprehend what that would mean. They have few legends of Arth, now and their stories are those of eternal sailors on the void between the worlds.