 The Templo Mayor archeological site and museum, is the center of the ancient teocalli, located now just northeast of the Zócalo.It was demolished by Hernán Cortés in the 1520s and its location forgotten.The exact site was determined in the beginning of the 20th century, but the decision to excavate was not made until 1978, when electrical workers chanced upon an eight-ton stone disk depicting the Aztec goddess Coyolxauhqui.