 This would later cause the Purépecha to deny the Aztecs aid in the defense of Tenochtitlan against the Spanish.The history of Michoacán has been studied from archaeological remains and other historical resources, such as the literary work "Relación de Michoacán" written in 1542, and it is known that the first settlers of the state were several Chichimeca tribes which arrived in different epochs and consequently evolved differently.The archeological sites found in the state, have helped clarify the history of the birth and development of ethnic groups which provided the essence of the Michoacán culture, dating back to the formative or Preclassical period (1500 to 200 BCE), the classical (800 BCE to 800 CE) and Postclassical (800 to 1000 CE), among whose sites are included