Tlacōpan

Tlacopan, "place on the rods" in Nahuatl and Abotto, "in the forest of trees", in Otomi, was a Tepanec city on the western shore of Lake Texcoco and the smallest partner of the Aztec Triple Alliance. It began as a subject of nearby Azcapotzalco, whose lord blockaded Tenochtitlan and drove Nezahualcoyotl of Texcoco into exile. Tlacopan broke with Azcapotzalco, and in 1427 it joined Tenochtitlan and Texcoco in the war that crushed the Tepanec capital the next year.

About 1430 the three remaining cities signed the treaty of the Triple Alliance. Tlacopan was given a fifth of the tribute from their joint conquests, against two-fifths each for Tenochtitlan and Texcoco. Under the alliance the Valley of Mexico's power reached the Gulf Coast and the Pacific, though Tenochtitlan gradually became the senior partner. In 1520, after the "Sad Night", Cortés and his battered army retreated to Tlacopan before making for Tlaxcala, and the Spanish returned to take Tenochtitlan in 1521.

The later city of Naucalpan de Juárez lies here.