The Brevity of Castles in the Sky

Through and through the horizon, 
Structures float in the sky. 
Little ships dock and unload their cargo, 
Maintaining the delicate symbiosis of land and air. 
They are immovable objects, akin to titans, 
Holding dominion over the boundless ephyr - 
Some are sheer cliffs of iron, 
Others, tiny fortresses of light.

A siren rings, ships scramble out, 
The watchtowers turn towards the unseen threat. 
One castle falls ejecting dust and smoke,
Drifting out of line as missiles bombard it's walls.
Another and another have fallen - 
A chain reaction of destruction,
Fueled by hatred of the surface.