Prior to the 18th century in Europe, people cooked over open fires fueled by wood. In the Middle Ages, waist-high brick-and-mortar hearths and the first chimneys appeared, so that cooks no longer had to kneel or sit to tend to foods on the fire. The fire was built on top of the construction; the cooking done mainly in cauldrons hung above the fire or placed on trivets. The heat was regulated by placing the cauldron higher or lower above the fire.