This is a real classic and a milestone in board game history.
Up to seven players control an ancient empire in the Near East. Goal of the game is to expand the empire, build cities and advance from the stone age to the iron age. A key factor is trading with other players. You try to collect goods, represented by sets of cards. You then may exchange these for cultural achievements.
Each area only supports a limited population. If the population grows beyond this limit, a conflict has to be resolved. This works really in a simple way : players remove alternately their pieces, starting with the less advanced player, until the limit is no longer exceeded.
You find a playthrough here.