Hello again, guys.
I was going to participate in "Before Columbus" challenge on PJ, but looking at the completeness of what I have I apparently fail to finish on time. So the best option left is to ask for advice here and do it properly.
So, here it is:

It`s much more serious than anything I tried before. I tried to make a composition, a perspective (3-point on the ziggurat, but 2-point on everything else, in fact). Everything is split in two in two directions: top-down and left-right.
Here it is with the vanishing points (the very first sketch):

I`ve never seen a drawing with anything situated beyond the vanishing points, and all my acquainted artists are too far so I could ask, so I had to improvise. There are no restrictions in the reality, right? There is panorama perspective (thing right out of hell). So, I`d like you to tell whether it`s wrong or very wrong here.

The palette:

I tried to do the "earth" palette which I was talking about in chatterbox: green shifted to brown and brown. I also added blue and red. Red looks a bit off as it doesn`t get shifted to brown: it stays red or becomes ginger. I spent a lot of time on the palette, and I like it, although it`s not perfect. May be it came out too dark. Do you think so?
Also I planned colour dichotomy (don`t look for it, I didn`t make it yet, and I`m not sure if I will manage to) to separate armies: the left one (conquerors) red-brown and the right one (defenders) green-brown, brown as the neutral colour.
Some global critique and advice would be nice to get before adding the details.
P. S. The tree on the right is a placeholder, I will define the shape and colouring later.