MEXICO CITY, Aug 11 (Reuters) - Mexico is building a towering replica of the Templo Mayor, the Aztec civilisation"s most sacred site, in the downtown of Mexico City to mark 500 years since the Spanish conquest of the Aztec capital, Tenochtitlan. The mostly white mock temple will be on show in Mexico City"s bustling main square, the Zocalo, close to the ruins of the real Templo Mayor, where the Aztecs venerated two main deities with elaborate pageantry and sacrificial offerings. The temple was destroyed by Spanish forces after their 1521 conquest and subsequent razing of Tenochtitlan, which became Mexico City. A colonial-era Roman Catholic cathedral was built next to where the temple once stood, using many stones from the toppled shrine. At 16 meters (52 feet) high, it will be the biggest ever replica of the Templo Mayor, according to Mexico"s culture ministry. Archaeologists say the original temple was as high as a 15-story building. read more "For the (Aztecs) it was the center of the universe. It was the point at which one could enter the underworld and the different celestial levels," said Argel Gomez, the ministry"s general festival director. Mexican President Andres Manuel Lopez Obrador on Friday will attend a ceremony at the Zocalo commemorating five centuries since the fall of Tenochtitlan to Hernan Cortes, the leader of the Spanish invaders. Lopez Obrador had previously sought an apology from Spain and the Vatican for human rights abuses committed during the conquest of what is modern-day Mexico.