Clash of Kings is an online mobile game, RTS real time strategy game, where players build an empire, and it involves elements such as city-building, castle defense, and conquering lands, is free to play on Android and iOS devices, from Elex.
Download the game at:
https://play.google.com/store/apps/details?id=com.hcg.cok.gp
https://itunes.apple.com/app/id945274928