Cannibals and Kings (15 page)

The next question to be confronted is how the Maya under the direction of their redistributor-chiefs managed to raise their population density to a level that was 250 times greater than that achieved in the interfluvial zones of the Amazon-Orinoco. Archaeologists have generally assumed that the ancient Maya farmed the Peten the way their modern descendants do—by means of the system known as slash-and-burn. But this is clearly an impossibility.

Slash-and-burn is a form of agriculture that is well-suited for regions that have abundant forest cover and high rates of regeneration. The object of the slash-and-burn system is to use a section of forest for a few years, let it lie fallow long enough for trees to grow back, and then use it again. “Slash” refers to the practice of cutting down small trees, vines, and shrubs and letting them dry before setting fire to them. The burning, usually carried out just before the onset of the rainy season, creates a layer of ash that acts as fertilizer. Crops are planted directly into the ash-covered soil in holes or small mounds without the need for tillage. High yields of corn, beans, squash, and other crops can be obtained for two or three seasons. Thereafter weeds spread from the surrounding uncut forest and infest the field; at the same time the ash fertilizer is leached away by rainfall. Soon a new plot must be found. Slash-and-burn agriculture is capable of high returns per acre and man-hour provided that an interval sufficient to permit a substantial regrowth of trees and shrubs is maintained between successive burnings. The greater the quantity of ash, the higher the yields. The longer the interval during which a forest is left fallow, the more wood there is to make ashes with. For this reason, slash-and-burn farmers in Southeast Asia think of
themselves as “the people who eat forests.” The shorter the fallow period, the lower the yields. In tropical forests the decline can be precipitous not only because the concentrated heavy rainfall rapidly leaches away the soil nutrients but because weeds grow thicker each year the field remains in continuous use.

Slash-and-burn was undoubtedly the system used by the earliest farming peoples who entered the Petén, but it could not have remained the principal mode of subsistence during and after the transition to the state. By counting the ruins of house sites, Dennis Puleston of the University of Minnesota estimates that there were 2,250 persons per square mile in the residential zone around Tikal and 750 persons per square mile in the zone between Tikal and its neighbor, Uaxactun. It is impossible for slash-and-burn systems to support such densities. Considering the entire Peten area, Sherburne Cook shows that enough maize, beans, and squash could have been grown with slash-and-burn techniques to support the estimated overall population of 1.5 million. But these calculations assume that the farmers were evenly spread throughout the forest and that they were free to move to new clearings as the old ones were exhausted. Neither of these assumptions is valid since the limiting effect of the dry season on the availability of drinking water is not taken into account. Furthermore, during the rainy season low-lying areas face the opposite problems—too much water—and are too swampy to be used without digging drainage ditches.

On theoretical grounds, the picture of what must have happened seems clear. As the population of the Peten increased, the slash-and-burn cycle must have been intensified, resulting in shorter fallows between burning and hence declining efficiency. This set the stage for the adoption and spread of a more efficient
system involving higher start-up costs, which in turn provided the basis for still higher population densities and the emergence of the first statelets. But what was the nature of the new and more productive system? I fear that my theory has run ahead of the archaeological facts, but there are some hopeful signs that the facts are about to catch up.

One of the measures taken by the Maya when the efficiency of slash-and-burn declined was to plant groves of breadnut trees
(Brosimum alicastrum)
. As C. L. Lundell pointed out back in the 1930’s, the breadnut is the most common tree covering the ruins of the Peten ceremonial centers. When archaeologists speak dramatically of having to hack away the jungle in order to expose the wonders of Maya architecture and sculpture, they generally neglect to say that they were hacking away at an overgrown orchard. Tree crops, of course, do have high start-up costs—one must wait several years before they begin to return the labor invested in them—but they are highly productive per acre and per man-hour. Recently, Dennis Puleston, having discovered that each house site at Tikal was surrounded by a grove of breadnut trees, reached the conclusion that breadnuts provided 80 percent of the calories consumed by the people of Tikal during the ninth century
A.D.
There are other alternatives, however, which may simply have been overlooked by the generation of archaeologists who preferred to think the Maya temples were let down from heaven on golden threads rather than built on the backs of people who wanted to know where the next meal was coming from. In this connection, one of the most important discoveries ever made about the Maya may prove to be the one made in 1975 by Ray Mathenay at Edzná in Campeche. Working with aerial photographs taken during the rainy season (others had limited
their aerial photography to the dry season, when conditions were “better”), Mathenay detected a network of canals, moats, and reservoirs radiating out from the ceremonial center. Because of the dense foliage covering them during the rainy season and the fact that the water in them dries up during the dry season, these constructions are difficult to detect from ground surveys alone.

The canals range up to a mile or so in length, a hundred feet in width and about ten feet in depth. Mathenay’s suggestion is that they were used for drinking water, for hand-watering adjacent gardens, and as a source of mud for renewing the fertility of fallow fields. I would add the implication that they enabled some regions to grow two crops a year, one based on draining low-lying areas during the rainy season and the second planted on wet mud during the dry season. While Edzná lies outside the central Peten area, the fact that its water control system remained undetected for so long means that all judgments concerning the absence of intensive systems within the Peten itself must be held in abeyance.

And this brings us to the most spectacular aspect of the Peten Maya. After
A.D.
800, in center after center, construction ceased, no more commemorative inscriptions were made, temples became littered with household rubbish, and all governmental and ecclesiastical activity in the Peten came to a more or less abrupt end. Authorities differ concerning how fast the population declined. But by the time of the arrival of the Spanish, the Peten area had long since returned to population densities at or below those characteristic of pre-state times and to this day the area remains virtually depopulated. Many other Mesoamerican pre-Columbian state systems, including Teotihuacan, suffered equally abrupt
collapses at one time or another. What is unique about the Petén Maya is that not only did the states permanently disappear but so did their entire populations. In the central plateau highlands political collapse was usually followed by the rise of new and larger states and empires embracing the territory and population of their predecessors. The implication of the Maya collapse, therefore, is that the Peten state developed on an unusually vulnerable ecological base which could not be regenerated once it broke down.

Exactly how the Maya destroyed their ecological base cannot be known until we have a better understanding of how the various components in their agricultural system fitted together. The best one can do for the moment is to say that each component had a limit to which it could be pushed, after which it would push back with devastating consequences. Short-fallow slash-and-burn can turn jungles into permanent grasslands. At the very middle of the Peten area is a huge, grassy savanna that was probably created by excessive burning. Deforestation leads in turn to erosion on hillsides. In the Peten the upland soil cover is extremely shallow and readily lost when not protected by plant cover. Erosion can also damage lowland water control systems since it leads to the build-up of excessive silt in canals and reservoirs. Finally, tampering with forest cover over an area as large as that of the Peten can easily change the regional pattern of annual precipitation, lengthening the dry season and increasing the frequency and severity of droughts.

The actual demise of each Peten center may have involved a slightly different scenario—crop failure and famine in some, rebellion in others, military defeat in still others, or various combinations depending on local events. But the underlying process undoubtedly involved
the depletion of fragile soil and forest resources to a point so low that centuries of disuse were required for their regeneration.

Whatever the precise cause of the Maya collapse, the reason for the preeminence of the highlands in Mesoamerica seems clear. The capacity of the semiarid valleys of the central plateau to undergo successive agricultural intensifications exceeded that of the Maya’s quasi-tropical forest. Let me show how this process of intensification operated in the history of the Teotihuacán empire.

The Teotihuacán Valley is a branch of the Valley of Mexico lying some twenty-five miles northeast of downtown Mexico City. Like the Tehuacán Valley, where the earliest domesticated plants were found by Richard MacNeish, the Teotihuacán Valley had no permanent villages until the first millennium
B.C.
Between 900
B.C.
and 600
B.C
. villages were confined to the forested upper slopes of the valley, below the early frost line but high enough up to take advantage of the extra precipitation which falls on the hillsides. The kind of agriculture practiced by these first villagers was undoubtedly some form of long-fallow slash-and-burn. By 600–300
B.C
. several larger villages had formed at lower altitudes at the edge of the valley floor, presumably to take advantage of the alluvial soils and to practice a rudimentary form of irrigation. During the next period, 300–100
B.C.
, settlements grew up squarely on the valley floor, and one of them—the nucleus of what was to become the city of Teotihuacán—already contained thousands of people. The movement from the slopes to the valley floor strongly suggests increasing reproductive pressures resulting from the intensification and depletion of the slash-and-burn system, especially from deforestation and erosion. As the labor efficiency
of slash-and-burn farming declined, it became worthwhile to expend start-up and construction labor on irrigation facilities. Numerous large springs fed by water percolating through the porous volcanic hillside to the valley floor formed the basis for the Teotihuacán irrigation system and are still in use today. As the population of the central settlement increased, the network of river-sized spring-fed canals was eventually used to water about 14,000 acres of highly productive double-crop farmlands.

The city of Teotihuacán grew rapidly after
A.D.
100, reaching a peak population of perhaps 125,000 people in the eighth century
A.D.
Careful mapping by René Millon of the University of Rochester shows that the city was divided into planned quarters and districts, each with its craft specialities, ethnic enclaves, temples, markets, palatial stone and plaster dwellings for the rich and powerful, and dark multi-family apartment houses for the populace—some 2,200 apartment houses in all. Millón has counted more than 400 workshops specializing in the manufacture of obsidian tools and more than 100 ceramic workshops. The largest and most ornamented buildings lined the huge stepped avenue which ran the length of the city almost two miles from north to south. The central monument—the so-called Pyramid of the Sun, built of stone-faced rubble—measures 700 feet to a side and rises to a height of 200 feet.

Around
A.D.
700 Teotihuacán suffered a cataclysmic collapse, possibly due to burning and sacking, associated with the rise of a new imperial power—the Toltec, whose capital was located a scant twenty miles away in the Tula Valley. The evidence is incomplete, but I propose that environmental depletion was primarily responsible. The volume of water issuing from the springs
fluctuates in relation to rainfall. A slight permanent drop in the volume of spring-fed water and in the water table underlying the valley floor would have compelled many people to move out of the city. We know that there was deforestation over an ever-widening perimeter as the city grew and consumed increasing quantities of wood for house beams and rafters, cooking fuel, and the manufacture of lime plaster. This deforestation was carried out on a sufficiently large scale to have altered the pattern of precipitation and runoff on the upper slopes of the valley.

There was one technical solution to the water problem which the people of Teotihuacán did not try except on a very limited basis. This consisted of using the shallow lake and swamplands that bordered the Teotihuacán Valley on the southwest and that in those days were probably linked to Lake Texcoco, a large, partly brackish body of water that filled most of the adjacent Valley of Mexico. To utilize the margins of the lake, it was necessary to dig drainage ditches and to pile up the excavated soil on ridges—a procedure which was much more costly than other forms of irrigation. Beginning about
A.D
. 1100 the high start-up costs of this form of agriculture could no longer be avoided by the people living in the Valley of Mexico. A network of drainage canals and highly productive ridges, whose fertility was constantly augmented by new dredgings, spread along the margin of the lake and provided the subsistence base for a half-dozen warring polities. One of these was the Aztec state, which would become the last American Indian imperial power in North America. Since the Aztec capital, Tenochtitlán, was located on an island connected to the shore by a causeway, the Aztecs enjoyed a military advantage over their neighbors and were soon in control of the entire lake region. As the
population grew to unprecedented densities, the ridged mounds were extended out into the lake itself by dumping mud on top of brush, corn stalks, and tree branches, resulting in fabulously productive
chinampas
, or “floating gardens” (which, of course, did not float).