Complex sentence: It was in Veracruz where he presided at the first mass that was done in Mexico, on April 21,1519, the same year as Hernán Cortés's mandate was venerated by the conquerors in the "Templo Mayor" of the Great Tenochtitlan.
Split into simpler sentences: It was in Veracruz where he presided at the first mass that was done in Mexico, on April 21 de1519. The same year, for Hernán Cortés's mandate, was venerated by the conquerors in the "Templo Mayor" of the Great Tenochtitlan.