The cultural fabric of the valley of Mexico was the product of the successive peoples which had settled there from the beginning of the early Pre-Classical period around 1800 BC until the time of the Aztecs.
The first significant sign of development was the construction, in the northeast of the valley, of the city of Teotihuacan, which in the early centuries of the Christian era saw the emergence of one of the most remarkable civilizations of Meso-America. Between 200 and 100 BC, the inhabitants of Teotihuacan raised the imposing pyramids of the Sun and the Moon along the Avenue of the Dead. Around these austere, geometric edifices, a great ceremonial centre and the biggest Meso-American city of the age were built.
The people of Teotihuacan had a calendar and a system of numbers, and practised a form of hieroglyphic writing. They made astronomical observations which they applied to the orientation of their monuments and their system of divination. They possessed notions of planning, the organization of urban settlements, and civil engineering. They knew the properties and medicinal uses of many plants. Their arts, especially architecture, low-relief sculpture, fresco painting and ceramics, were distinguished by a style that was sober but also highly expressive and rich in symbolism. They worshipped Quetzalcoatl, the plumed serpent, and their cosmogony had an important influence on later cultures.
Then came decline. Between 650 and 700, the city seems to have been looted and demolished. Around 726, groups of people from a mysterious place called Tamoanchan arrived in the valley, and ceremonies to celebrate the coming of the Fifth Sun were held in the sacred city in 751. This date marked the beginning of a new historical era, that of the Toltecs. The Toltec period, which reached its apogee between 752 and :[200, was regarded in later centuries as a legendary period of peace, abundance and development of the arts, crafts and sciences.
After long wanderings from a region called Aztlan or "place of herons", the Mexicas (or Aztecs as they are generally known) settled on an island on a lake in the central valley of Mexico. In 1325, on the order of their tribal divinity, Huitzilopochtli, they rounded what was to become the powerful city of Tenochtitlan, whose splendour captivated all who set eyes on it.
This nomadic tribe mercilessly extended its control over the neighbouring peoples. Its dominion covered the central and eastern region of present-day Mexico, and it established enclaves on the Gulf of Mexico and the Pacific Coast. But there were still pockets of resistance within this territory, and the hostility of the peoples who lived in them, above all those of what is today the state of Tlaxcala, would play a decisive role in the Spanish conquest.
The Aztec empire, or CulhuaMexica, was based on a triple alliance between Tenochtitlan, Texcoco and Tacuba. At the end of the fifteenth century it controlled some thirty-eight provinces extending over almost half a million square kilometres, a quarter of the area of modern Mexico. Nahua was the lingua franca and the people shared common religious practices.
Estimates of the population of central Mexico when the Spanish arrived have ranged from 4.5 million to 25.2 million. For Tenochtitlan the figures vary between 72,000 and 300,000.
The vast empire the Aztecs governed from their little island was highly organized. Tribute in food, clothing and precious objects from the subject peoples reached the capital by water across the lake or over causeways. Thousands of people thronged the city's great markets, where a huge variety of products could be found. The right to own property was guaranteed, and priests and warriors occupied privileged positions within the castes. Everything that had been created by the people of Teotihuacan and the Toltecs was taken to a high degree of development by the Aztecs: calendar systems and astronomical calculations, techniques of civil engineering and urban planning, education, the preparation and interpretation of historical books and rituals, cosmology and religion, methods of divination, arts and crafts. However, Aztec society at every level was permeated by a messianic religion which provided a pretext for imperial conquest and a justification for human sacrifices, which were deemed necessary to nourish the life of the Sun through blood.