Roderick's Travels
an excerpt

I began to imagine what I would find when I reached the city in the distance. From deep in my world history class, I remembered the tales of the once great cities of men that littered the land. It was here that the flying cities were built and first lifted into the air. My teachers once told me that they were filled with the knowledge of the ages, of amazing machines that would talk and walk and work as servants and some even as the equals of men. Clockwork machines that could think for themselves.
There were libraries as large as Zyl, where all the knowledge of humanity had been stored. The mysteries of the ages had been laid open, and humanity was at it's zenith. Life was good and easy, and much art was created. I have heared small snippets of the music that was written then, themes passed down over many hundred generations, and still it is the most beautiful sounds I have heard. To think that with all of this amazing prosperity, the nations of earth still feuded and warred amongst themselves.
My mind drifted from that to the thought of the great death that came when the armies of the earth unleased their most potent weapons upon each other. Luckily the knowledge of such weapons was lost to the ages, but their power was devistating. They scorched the world, destroying all life on the land and in the seas. Billions of innocent people died. Only those in the flying cities survived, and only by climbing so high that they were above the majority of the effects of the war. For many generations, those in the skies lived high above the clouds, high enough to see the curve of the earth itself. Those that didn't gain enough altitude quickly succumbed to the toxins in the air, leaving floating ghost cities that could be seen from those above. Those who made the climb lived off the oxygen they collected and contained in chemical form. Life was hard for many generations. It was during this time that the beginnings of lightning farming were tried, to rejuvinate the electrical storage devices that once kept the cities aloft.
Meanwhile, on the surface, almost all of mankind had been killed off. The great cities became graveyards, littered with the bones of the dead. The sun had been blotted out by the dust kicked into the atmosphere, and clouds formed from where the vaporized seas once stood filled. The living machines continued to battle, until they too came under the influence of time and ceased to fight, slowly rusting away in their shining battle armors. And so the world moved on, and those of us living above the clouds learned how to cope without solid earth to work and live on.
Over time, those in the skies learned the power of steam, and how to turn the basic elements of air and water around us back into those things we needed, fuel and food. As generations passed, the cities were modified with this new technology. A byproduct of this was that the cities had to fly lower for much of the time. Luckily, over the few hundred years since the war, the toxins had fallen, and the air was mostly clear.
Most of the dead cities had fallen to the earth, but a few remained aloft. Brigands and warlords quickly resettled these when they were outcast from their own cities. Using stolen technology, these ancient cities were brought back to working condition and used to wage war upon the free cities of the air. This was the First Aerial Wars. The battles were fierce and even more of the cities of the air were knocked from their airy perches, but eventually the free cities drove the warlords to the most desolate and distant reaches of the skies.