During the Tzacualli ceramic phase (ca. 1–100 CE), the city of Teotihuacan continued its rapid growth. It expanded to cover about twenty square kilometers. I estimate its population by the end of this phase as perhaps around 60,000 to 80,000 – that is, three to four times the population at the end of the Patlachique phase. In absolute numbers, this is an increase of somewhere between 40,000 and 60,000 persons. But because the starting population was so much larger than at the onset of the Patlachique phase, it represents a considerable slowing of the growth rate. It had averaged at least 1.5 percent per year but now averaged not more than 0.9 percent. Probably much of the increase continued to be due to migration, since this is the time when population appears to have declined markedly elsewhere in the Basin of Mexico. Sanders et al. (1979: 105–108) found a dramatic decrease outside the city in this period, although probably not as great as the 80 to 90 percent once thought (Sanders, personal communication 2006; Parsons 2008). However, Tzacualli ceramics are derived from those of the Patlachique complex and do not differ enough to suggest any sizable influx from far outside the Basin.

The areas of highest sherd density in the city (Figure 5.1) remained in the northwest, although density decreased on the slopes of Cerros Colorado and Malinalco and increased in the zone centered on sectors N5W2 and N4W2, which expanded somewhat to the west and north to include sector N6W3. Density was only moderate along most of the northern Avenue of the Dead (possibly many of the sherds in this area were incorporated in the fill of the Sun Pyramid). There is a small density peak in the area of the later Ciudadela complex, where there are remains of pre-Ciudadela structures that were completely razed when the Ciudadela was built. Farther to the south and east, light to moderate Tzacualli sherd cover extends over most of the entire area of the later city. The scale of the great pyramids suggests powerful and highly centralized authority.