it's a long time I wanted to make a tutorial to show the steps of my work, but usually I trash them and forgive to save them. I really like to "flatten down" my layers every so often, because I don't want to "turn back" and prefer to repaint the parts of the painting I want to change. I don't know if this tut can be useful for someone, but it was funny for me to illustrate my worksteps.
Anyway, to the tutorial: the initial idea after this painting was to create a representation of Atlantis that could be used both as a poster/painting, and as a fantasy rolplaying and writing reference for "atlantis adventuring".
I had a clear idea of the basic shape of the city, and of the major features: the fortified sea gates, the canals, the bridges, the cultivated fields, the Imperial palace, the temples, and the mountain in the center of the city.