Tenochtitlán

Built in 1325, Tenochtitlán was the capital city of the ancient Mesoamerican civilization of the Aztecs. Its peak population of approximately 200,000 people put it in the rankings of one of the largest cities in the world at its time.
Legend tells us that Aztec god Huitzilopochtli inspired the construction of the mega-city on the marshy, salty Lake Texcoco. The lake was shallow enough to allow the Aztecs to create a base of support for their city with a mesh-like combination of mud, reeds, and tree roots. Gradually, the soil concoction settled enough to form a stable island on which they constructed their city. They used this same principle to create “floating” gardens, called chinampas. These gardens granted the city a successful and reliable source of food. Two main aqueducts supplied the city with fresh clean drinking water.
Three main causeways, facing north, south, and west, connected the city to the mainland. Half land, half water canals made up the roadways of the city; the typical mode of transportation through these canals was small canoes. The canals also served as part of the city’s structural defense system. The city was known throughout Mesoamerica for these defensive properties, its organization, and its cleanliness.
The impressive architecture of Tenochtitlán also symbolized great wealth and power throughout Mesoamerica. The various pyramids, temples, and busy markets were very colorful and were designed in a unique artistic fashion. The Temple Mayor and the temple of Quetzalcoatl are two of the better-known religious structures to the modern world. Both were located in the centralized Sacred Precinct of the city, which could hold more than 8,000 people at any given time. This district housed the temples for the most important Aztec gods, as well as ball courts for entertainment, housing for the temple priests, and schools for educating the youth.
August of 1521 marked the downfall of the Aztec population. While European diseases, brought to Latin America by the Spanish Conquistadors, wiped out much of the population, Hernan Cortez’s invasion of the city led to its ultimate destruction. Cortez and his men flattened the city and built a new Spanish city overtop; today this city still stands, known to us as Mexico City.

References:
http://www.mnsu.edu/emuseum/archaeology/sites/meso_america/tenochtitlan.html
http://www.mexicocity.com.mx/anc_city.html
http://www.metmuseum.org/TOAH/hd/teno_1/hd_teno_1.htm