The Aztecs traveled for many years until they found the sign that they were looking for, an eagle sitting on a cactus eating a serpent. They found it on the shores of Lake Texcoco. This was the 13th century, and they were among the last of the Nahua tribes to arrive in the Valley of Mexico. The Aztecs found the valley to be heavily populated. Their homeland at this time was only two small mounds that barely emerged above the waterline. The first thing the Aztecs did was build a shrine for their god Huizilopochtli. The first Aztec homes were reed huts. All around them were marshes. The entire Valley of Mexico at this time was covered in a series of shallow lakes. Most goods and people moved by canoe. Cities were built on both land and water. Near the location where the Aztecs chose to live there were no building materials, or arable land. Gradually, the city of Tenochtitlan grew by using a system called chinampas or floating gardens. At this time, there were approximately fifty cities in the Valley of Mexico. This would have made this area one of the most heavily populated in the world.
From 1427 to 1440, King Itzcoatl ruled the Aztecs. He conquered Azcapotzalco and founded the Triple Alliance of Tenochtitlan with Tetzcoco and Tlacopan. Itzcoatl was followed by King Montezuma I who conquered lands in all directions. For the first time human sacrifices were performed in the Temple Mayor, or Coatepec (Serpents Hill) as the Aztecs called it. Templo Mayor was the center of the Aztec underworld. According to religious theory, blood had to be spilled so that the cosmos would continue to exist. The sun required human hearts and blood so it could continue to shine.
Three causeways connected Tenochtitlan to the mainland. The causeways controlled the water levels of various lakes. However, flooding occurred between the years of 1440 and 1450. The Aztecs solved the problem of flooding by building a 17 mile long dyke. The dyke divided Lake Texacoco into two parts. As the city grew so did the demand for water. Eventually, water had to be brought in by aqueduct from springs near Chapultepec. The soil around Tenochtitlan was not very good so sometimes the food had to be brought in from great distances.
Most of the buildings in Tenochtitlan were single story and painted white. However, the higher the social order, the more likely that they would have two stories. In all, there were an estimated 60,000 dwellings with about 250,000 people inhabiting the city limits. The largest market was on the Plaza of Tlalteloco. On normal days the market had between 10,000 and 20,000 visitors. However, every fifth day the crowd reached 50,000. People came and went all day long. Buying and selling in the marketplace was a way of life. People used cacao, woven cloth, and gold grains as currency. As they still do today, many women walked through the city streets carefully balancing baskets of vegetables and poultry on their heads. At the same time, men carried enormous loads of commerce on their backs. Canoes and walking were the two modes of transportation and they were treated equally.