[FROM: Timo Roth]
for mesopotamian Princes will be here the solution (I think you already have the chinese Seal):
1st: you need to move to the meseopotamian area.
2nd: clear all tiles till you see a stair downward to their 2 Graves (left & right)
3rd: awake them
4th: move 3 stones at the outer left and right side one level higher where the Stairs are
5th: if you have open all 6 Watergates the Princes will appear in the top mid - see screeny: