María Elena Morales Osorio, 50, (kneeling) and Israel Salinas Ortiz, 25, (standing) welcome new dancers to a weekly dance performance in Mexico City’s Zócalo, or city center, that celebrates the people and traditions of the eras that precede the Spanish colonization. The group meets on Fridays and Saturdays. Every 20 days, participants dress in traditional clothes, in accordance with the Aztec calendar’s 20-day month. Morales Osorio has been the dance’s caretaker for 20 years.