At the end of each 52-year cycle that governed their calendar, the Aztecs would put out all the fires they burned for everyday use, and as night descended, priests would use a friction rod to ignite a new blaze atop a sacred volcano that soared over the surrounding shimmering lakes. The event involved the burning of a human sacrifice and culminated in runners carrying torches lit by the fire back down the mountain to relight hearths in temples and in every home.