It has been said that the measure of the Maghreb (the west) is couscous. There is an invisible culinary line somewhere in Libya separating couscous eating North Africans from the rice eating Arab Mashriq (the east).
The culinary difference here is not merely of basic starch. The cooking technique for couscous (steaming) informs the entire cuisine. North African cuisine is sauce driven and there is an overall preference for moist heat cooking methods. Tagine cooking is all about controlling heat and moisture.
The word couscoussier is a French word derived from North African kiskas, which refers only to the steamer insert. The pot itself is called a gdrah and the soup or stew cooked in it, over which the couscous grains or pasta steam, is called marga or tagine. Couscous is also steamed over plain water. There is no special occasion or holiday without couscous.
This ingenious method of cooking allows for two dishes to be cooked over a single source of heat, a very important feature in a region that has historically dealt with cooking wood shortages. Some couscoussiers have two stacking steamer inserts. Couscous grains or pasta are usually steamed two or three times. Steaming grains such as bulghur, quinoa and millet produces a lighter, fluffier and more elegant finished product than boiling does.