SACRED CITIES: Mexico City: The Promised City of Huitzilopochtli. In the time before history, the god Huitzilopochtli informed the ancient Aztec king that he would indicate the location of their future sacred city. For centuries they wandered the Americas until they saw an eagle perched on a cactus with a serpent in its mouth. This was the sign promised by Huitzilopochtli. The Aztecs built one of the most glorious cities on the earth there; by 1500 it was three times the size of London. The Spanish conquered the city in 1521. Again a deity appeared to the Aztecs, this time in the form of Mary, the mother of Jesus. At Guadalupe, Mary took the form of a dark-skinned Indian woman and spoke to the Aztec peasant Juan Diego in Nahuatl and informed him that the Aztecs were still the chosen people of god and Mexico City was still Heaven’s sacred city. Mexicans today still venerate Our Lady of Guadalupe and make pilgrimages to her shrine. Dr. Ronald Brown will recount his experiences in this sacred Aztec and Catholic city. Next month: Benares on February 1. Sponsored by the Friends of the Library. 3 p.m.