context: The earliest Finnish saunas were Bronze Age (1500-900 BC) saunas. The sauna was a pit dug in the ground, with a pile of stone at the bottom. After the stones were heated, the pit was covered with pulleys, turf or peat. Water was poured on the stones and the steam was heated by the steam. [6]
question: When was the sauna invented?
answers.text: 1500-900 BC