As part of the commemoration of the 500th anniversary of the fall of Mexico-Tenochtitlán before the Spanish conquerors, CNN had exclusive access to an underground archaeological research zone in the Historic Center of the country's capital.
Rey Rodríguez went down to the bowels of Mexico City to learn how the remains of the Huey Tzompantli are studied, a structure made up of human skulls that the Mexica used to honor the gods through sacrifices.