In primitive, hunter-gatherer cultures, there was no division of labor. But every civilization since has had a worker "class," devoted to the production of goods and the unskilled tasks necessary for the maintenance of society. In most early societies, slaves and peasants fulfilled this role. With the coming of the Middle Ages, the more specialized workers organized themselves into craft guilds. The technological advances of the Industrial Age gave rise to a new class of semi-skilled workers: wage laborers, most of which worked in factories and offices. Continuing trends in the specialization and professionalism of labor during the late 20th century has not altered the fact, however, that civilization still rests upon the shoulders of those who till the fields and build the roads.