Nomadic Finnish, Swedish and Norwegian people are believed to have built saunas over 2000 years ago, dug into a hill or embankment. Later saunas were later built as huts using wooden logs. Rocks were heated in a fireplace. The smoke was then allowed to escape and water was poured on the hot rocks to create steam. The steam causes perspiration and flushes toxins from the skin. Smoke saunas were made common until the twentieth century. They were then replaced with purpose-build wooden structures with iron stoves and metal chimneys. Modern saunas tend to use electric heaters. They are built in apartments for everyday use. The art of building wood-heated saunas is being revived, often in a garden location and in conjuction with a cold swimming pool.