It's going to take some time to imagine what is going on here. It looks like the dark lord of something-or-other is using his monster army to destroy a city? So, what is the machine in the sky? The defenders' capital ship, perhaps? Or the gate by which he got there?
Just FYI, I've had this in my favorites for a while, so it's why when I spotted it on an album cover for this band Dol Ammad, I knew right away what it was. Just letting you know in case it's been stolen.