These trends continue throughout Monte Albán Late I with the Valley as a whole growing to an estimated population of more than 50,000 people, more than a third of which (17,000) lived at Monte Albán and two thirds (33,000) of which lived within 20 km of the site.
Since the estimated population growth over this time period translates into a growth rate greater than observed natural growth rates for human populations, it is assumed that immigration was responsible for much of the growth.
During Monte Albán Early I, as in earlier times, most settlements, with the exception of Monte Albán and its immediate vicinity, are located close to the alluvial plain of the Rio Atoyac and its tributaries. But, during Monte Albán Late I, most of the new settlements appear in the piedmont -- apparently a somewhat less desirable location for agriculture. Hilltop sites with agricultural terraces on the hillsides (much smaller, but morphologically similar to Monte Albán) appear in significant number in Late I.
Cultivation and subsequent abandonment of the agriculturally marginal piedmont zone, the so-called piedmont strategy, is a recurring feature of settlement in the Valley of Oaxaca. The term ‘strategy’ is possably misleading in that might suggest a deliberate decision of political leaders to undertake agriculture at these locations. While this is surely possible, it is also possible that individual households simply moved into the piedmont . locations without central direction, possibly just because all the “bottom land” was already taken. However the decison was made, in view of the evidence for immigration (See above.), it is likely that the households occcupying these locations were latecommers to the Valley.
By the Monte Albán Early I phase, many residential structures are constructed of adobe and/or stone, in contrast to the waddle-and-construction of earlier times.
