Valley of Mexico

The Valley of Mexico (Spanish: Valle de México; Nahuatl languages: Anahuac, lit. 'Land Between the Waters') is a large bowl-shaped area on high flat land in central Mexico. Surrounded by mountains and volcanoes, this valley was very important to many ancient peoples, including the Teotihuacan, the Toltec, and the Aztec Empire. Today, the valley is mostly covered by Mexico City, the capital of Mexico.

Long ago, the valley had five shallow lakes—Lake Zumpango, Lake Xaltocan, Lake Xochimilco, Lake Chalco, and Lake Texcoco. When Spanish explorers arrived in 1519, many people lived here. After the Spanish took control, they drained the lakes to stop floods. By the 1900s, the lakes were almost gone, and the city grew over the land where the lakes used to be.

The valley is located in the Trans-Mexican Volcanic Belt and has many people living in it today. It stretches about 125 kilometers long and 75 kilometers wide. Even though it is high up—about 2,200 meters above sea level—it has a comfortable climate that helped people live there for thousands of years. Today, around 21 million people call the valley home, making it one of the biggest cities in the world.

Because so many people and factories are in the valley, the air and water face big problems. Pollution often stays trapped, and taking too much water from underground causes parts of the city to sink. Engineers have had to build new tunnels and canals to help manage the water and keep the city working.

History of human habitation

Main article: History of Mexico

The Valley of Mexico attracted early humans because it had plenty of plants, animals, and good land for farming. People in Mesoamerica, including central Mexico, began farming between the end of the Pleistocene epoch and the start of the Holocene. The oldest known settlement in the valley is in Tlapacoya, near where Lake Chalco once was. Evidence shows people lived there as far back as 12,000 BC. After 10,000 BC, more tools and objects were found, showing more people lived there.

Giant Columbian mammoths once lived in the area, and many mammoth bones have been found near where Lake Texcoco was. These bones are still found sometimes in fields and during construction. The richest collection of mammoth bones is at the Paleontological Museum in Tocuila near Texcoco.

Tlatilco was an early village near today’s Mexican Federal District, and it flourished between 1200 BC and 200 BC. People there grew beans, amaranth, squash, and chili peppers.

After Tlatilco, Cuicuilco became a city by 1200 BC but declined around 100 BC to 150 AD after a volcanic eruption.

Around 2,000 years ago, the Valley of Mexico became very crowded. Teotihuacan grew into a large city around 800 BC and became very important by 200 BC, with about 125,000 people. Later, the Toltec people rose to power, and Teotihuacan declined.

After the Toltecs, new cities grew around the lakes. The largest was Tenochtitlan, founded in 1325. It used special farming islands called chinampas to grow food. Tenochtitlan became powerful and formed alliances with Texcoco and Tlacopan. When the Spanish arrived in 1519, Tenochtitlan was the leading city.

By 1520, the valley had over 1,000,000 people.

After the Spanish conquest in 1521, Tenochtitlan was rebuilt as Mexico City. The city grew as the lakes got smaller. By the early 1900s, Mexico City's population had reached over one million. Growth continued, especially after independence, with more people moving in and new infrastructure being built.

Mexico City faces air pollution challenges due to its height and surrounding mountains. The valley traps pollutants, which can affect health. While improvements have been made, fine particles are still a problem.

Hydrology

The Valley of Mexico is a special kind of valley called an endorheic basin. It has three areas: a low plain that once held lakes, a middle area called the piedmont, and surrounding mountains. Rain and melting snow from the mountains flow into the valley, creating springs and water sources.

Before the 1900s, the Mexico City area had several lakes. These included Zumpango, Xaltoca, Xochimilco, Chalco, and the largest, Texcoco. Together, they covered about 1,500 km² (580 sq mi) of the valley floor. Over time, the lakes shrank because of climate changes that brought warmer temperatures and less rain.

Humans have managed water in this valley for thousands of years. The Aztecs built walls to control flooding and separate different types of water. After the Spanish arrived, they continued these efforts. Major projects to drain water began in the 1600s to stop flooding in the city. These efforts continued into the 1800s and 1900s, with large canals and tunnels built to move water out of the valley.

Because much water has been taken from underground sources, parts of Mexico City are sinking. This sinking causes problems with flooding and damage to water systems. Efforts continue today to manage water and stop further sinking.