The rise and fall of Teotihuacán is almost exactly contemporary with imperial Rome. There is evidence of small agricultural communities in the vicinity dating to around 600 BC; by 200 BC a township had been established on the present site. From then until 1 AD (the period known as the Patlachique phase) the population increased, and the city assumed its most important characteristics: the great pyramids of the Sun and Moon were built, and the Calzada de los Muertos laid out. Development continued through the Tzacualli and Miccaotli phases (1–250 AD) with more construction and the blossoming of artistic expression. Then through the Tlamimilolpa phase (250–450 AD) there is evidence of the city’s influence (in architecture, sculpture and pottery) occurring at sites throughout modern Mexico and into Guatemala and Honduras. From 450 to around 650 AD (Xolalpan phase) it reached its peak in both population and power, with much new building and addition to earlier structures.
Already by the end of this period, however, there were signs of decline, and the final phase, the Metepec, lasted at most a century before the city was sacked, burnt and virtually abandoned. This may have been the result of invasion or internal strife, but the underlying reasons could have been as much ecological as military. Vast forests were cut down to build the city (for use in columns, roof supports and door lintels) and huge quantities of wood burnt to make the lime plaster that coated the buildings. The result was severe soil erosion that left the hillsides as barren as they appear today. In addition, the agricultural effort needed to feed so many people (with no form of artificial fertilizer or knowledge of crop rotation) gradually sapped what land remained of its ability to grow more.
Whatever the precise causes, the city was left, eventually, to a ruination that was advanced even by the time of the Aztecs. To them it represented a holy place from a previous age, and they gave it its present name, which translates as “the place where men became gods”. Although Teotihuacán features frequently in Aztec mythology, there are no written records – what we know of the city is derived entirely from archeological and artistic evidence, so that even the original name remains unknown.