With the magical engines in place, the dragonborn now had a fleet of airborne attack platforms with which they could assault the aeries of their enemies. Their first attempt ended in disaster. They did not know how to fight battles in the sky. Their enemy, who was a creature that spent it’s life in the sky, was too maneuverable and too well versed in aerial combat. Though the sky ships were formidable, the enemy was able to bring many down preventing them from reaching the home aeries and off loading their troops. They needed something larger and more difficult to attack that would allow them to carry their assault troops to the high places of their enemy. The eventual result was the flying city.
Drawing on the creation ritual bestowed by their goddess, the dragonborn magi increased the scale to create larger and larger versions of the engines. Eventually they created an engine that was capable of lifting incredible volumes of earth. By combining the effects of many of these new and larger engines, they were able to lift an area nearly a mile in diameter. This was the first of the great flying islands. Now they were able to carry an entire army to their enemies. The new strategy worked well and within a generation the dragonborn were victorious.
With time they perfected their technique to the point that they had increased the size of their islands to several miles. this allowed them to carry more than just troops. They carried enough land for livestock, farming and even maintaining forest lands. In this way the cities became nearly self sufficient.