Rose medals are needed for the first promotions. You receive cross medals from attacking low level valleys. You usually receive cross medals when attacking level 1 through level 4 valleys. Reports from some players say that you can also find rose medals occasionally in mid level valleys level 5-6. (I’m not sure if this is a valid claime or not.)
You need 5 rose medals to promote your rank to Major.
I KNOW some of you are mad right now because you cannot find Rose medals. It appears to me that Evony has changed the drop rate of medals (at least one new servers). It can take easily take 50 or MORE attacks to find one medal. I do not know why. I do not know if this is a bug or not but I will keep you posted as I get more information.