The introduction of smallpox among the Aztecs has been attributed to an African slave (by the name of Francisco Eguía, according to one account) but this has been disputed. From May to September, smallpox spread slowly to Tepeaca and Tlaxcala, and to Tenochtitlán by the fall of 1520. At this time, Cortes was returning to conquer the city after being thrown out on the Noche Triste. Cortes names only one indigenous leader who died of smallpox, Maxixcatzin. However, Cuitláhuac and other native rulers also died of smallpox. Chimalpahin reports the death of some lords in Chalco from the disease as well. These deaths were part of a widespread epidemic which decimated the common population. Estimates of mortality range from one-quarter to one-half of the population of central Mexico.