Tlatelolco (Classical Nahuatl: Tlatelōlco [tɬateˈloːɬko], modern Nahuatl pronunciation ) (sometimes also called Xaltelolco) was a pre-Columbian Nahua altepetl (town, city) in the Valley of Mexico. Its inhabitants were known as Tlatelolca. The Tlatelolca were a part of the Mexica ethnic group, a Nahuatl speaking people who arrived in what is now central Mexico in the 13th century. They settled on an island in Lake Texcoco where they founded their city on the northern part — the other Mexica group, the Tenochca, founded their city Tenochtitlan on the southern part. The city was closely tied with its sister city, which was largely dependent on the market of Tlatelolco, the most important site of commerce in the area.

The Tlatelolco archaeological site is an archaeological excavation site in Mexico City, where the remains of the pre-Columbian city-state of Tlatelolco have been found. It is centered on the Plaza de las Tres Culturas, a square surrounded on three sides by an excavated Aztec site, a 17th-century church called Templo de Santiago, and the modern office complex of the Mexican foreign ministry. In February 2009, the discovery of a mass grave with 49 human bodies was announced by archaeologists. The grave is considered unusual because the bodies are laid out in ritual fashion.

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