With the advent of the chimney, the hearth moved from the center of the room to one wall, and the first brick-and-mortar hearths were built. The fire was lit on top of the construction; a vault underneath served to store wood. Pots made of iron, bronze, or copper started to replace the pottery used earlier. The temperature was controlled by hanging the pot higher or lower over the fire, or placing it on a trivet or directly on the hot ashes. Using open fire for cooking (and heating) was risky; fires devastating whole cities occurred frequently.