On left is 'Piedra de los Sacrificios', an Aztec sacrificial stone thought to have been used at Tenochtitlan for human sacrifice. Uncovered in the capital's rubble, it is believed to have been disposed of during a New Fire Ceremony at the close of a 52 year cycle. In the 1930s anthropologist George C. Vaillant proposed that these "dumps" were visible at the household level. Scoffed by his colleagues it was not until 2001 when his theory was revisited and published.