The Plaza de Las Tres Culturas is the main square of the Tlatelcolco neighborhood of Mexico City. The name signifies three periods in Mexican history, pre-Columbian, Spanish colonial era and the independent nation. The square was completed in 1966 and is flanked by the Tlatelcolco ruins, a 1960's housing complex, the collage of Santa Cruz de Tlatelcolco and a church built from Tlatelcolco Temple stones.
On October 2, 1968, Mexican Armed Forces opened fire on a group of unarmed civilians on the plaza who were protesting the upcoming 1968 Summer Olympics. The Mexican government and media claimed that the Armed Forces had been provoked by protesters shooting at them, but government documents made public since 2000 suggest that snipers had been employed by the government.
Twenty five people were officially reported dead. Later investigations identified 44 remains. Eyewitnesses claim that over 300 bodies were carted away from the square. The real death toll remains a mystery.
Read more here: What really happened? Mexico 1968 Massacre