Louvers come from the Middle Ages as lantern-like constructions in wood that were fitted on top of roof holes. They were put in large kitchens to allow ventilation while keeping out rain and snow. They were originally rather rough constructions consisting only of a barrel. Later they became more elaborate designs made of pottery. They took the shape of faces where the smoke and steam from cooking would pour out through the eyes and mouth. They also became more like modern louvers, with slats that could be opened or closed by pulling on a string.