Wikipedia on the city:
The city was connected to the mainland by bridges and causeways leading to the north, south, and west. The causeways were interrupted by bridges that allowed canoes and other water traffic to pass freely. The bridges could be pulled away, if necessary, to protect the city. The city was interlaced with a series of canals, so that all sections of the city could be visited either on foot or via canoe...The city was divided into four zones, or camps; each camp was divided into 20 districts ; and each calpulli, or 'big house', was crossed by streets or tlaxilcalli. There were three main streets that crossed the city, each leading to one of the three causeways to the mainland of Tepeyac, Iztapalapa, and Tlacopan. [An expert] reported that they were wide enough for ten horses. Surrounding the raised causeways were artificial floating gardens with canal waterways and gardens of plants, shrubs, and trees. The calpullis were divided by channels used for transportation, with wood bridges that were removed at night....In the center of the city were the public buildings, temples, and palaces. Inside a walled square, 500 meters (1,600 ft) to a side, was the ceremonial center. There were about 45 public buildings, including: the Templo Mayor, which was dedicated to the Aztec patron deity Huitzilopochtli and the Rain God Tlaloc; the temple of Quetzalcoatl; the tlachtli (ball game court) with the tzompantli or rack of skulls; the Sun Temple, which was dedicated to Tonatiuh; the Eagle's House, which was associated with warriors and the ancient power of rulers; the platforms for the gladiatorial sacrifice; and some minor temples.