Our investigation of the development of science and its interaction with civilization and society has now reached the stage where contact was established between the civilizations of the "Old World" and those of the "New World." From this point on the history of civilizations and science is a global history, in which every new development affects all continents. Before we enter this global history it is appropriate to establish the state of knowledge and the role of science in the civilizations of America, civilizations that were isolated from the accumulated knowledge of Africa, Asia and Europe.
The great American civilizations were confronted with much harder conditions than the ancient civilizations of the Indus valley, Mesopotamia and Egypt, which developed in parallel with each other and established contacts between each other at a very early stage. The exchange of knowledge, particularly in the form of transfer of inventions, was an important ingredient of their development.
The American civilizations arose on an isolated continent and had to be much more self-sufficient. We know from Lecture 2 that Caral, the first major American civilization, developed not much later than the civilizations of Mesopotamia and the Indus valley. At the arrival of the European conquistadores the American civilizations had reached a stage of development comparable to Egypt at the time of Alexander the Great, a stage where the distinction between science and religion was still quite blurred and scientific work was the responsibility of priests.
In the context of a global history of science a detailed review of the organization and development of the American civilizations prior to the arrival of Europeans (usually referred to as "pre-Columbian civilizations") does not add much information, and this chapter will therefore be brief. But it would do serious injustice to the people who created the American civilizations if we were to ignore their achievements altogether.
The major lesson that can be learned from pre-Columbian history is the importance of inter-civilization contact for the development of science. Our experiment of Lecture 4 already demonstrated that the intellectual capacity of people from 4,000 years ago was the same as that of the people of today. The fact that the pre-Columbian civilizations lagged Asia and Europe in their development by some 1500 years can therefore not be ascribed to an intellectual inferiority of the American people, although the European conquerors often used this argument as an excuse for their treatment of "the natives." Who can tell today how much or how little the Roman civilization would have achieved without access to the invention of the wheel in Sumer, the shipbuilding skills of Crete and the astronomical knowledge of Egypt?
As far as we know no major civilization developed in North America. Trade routes existed across the entire continent, and some people developed an urban society, the most prominent being the Anasazi. The Spanish invaders called them "Pueblo" (Spanish for "village" or "town."). During the 11th - 14th centuries the Anasazi built large cities and religious centres and must have had advanced division of labour. Indications for a similar society exist in the lower Mississippi River region. But these societies went into decline before the arrival of the Europeans, and when the Spanish arrived the Anasazi lived in small villages and were occupied with subsistence agriculture.
Civilization in Meso-America (the region from Mexico to Guatemala, Belize and parts of Honduras and El Salvador) began with the Olmec civilization that arose in north eastern Mexico around 1150 BC. The Olmecs were followed by the Zapotecs, who established their capital Monte Albán in central Mexico, and the civilization of Teotihuacán near today's Mexico City. Around 900 AD the Mixtec empire assimilated the Zapotecs, and according to ancient American tradition the Toltec established an empire shrouded in mystery around their capital Tollan (Tula).
Ancient annals assign to the Toltec the role of first great city builders and civilizers of Mexico, and several later rulers claim them as ancestors. At the time of the arrival of the Spanish invaders the dominant civilization of Mexico was that of the Aztecs, who ruled over an empire of some 5 million people. The Aztecs, warrior nomads who called themselves Mexica, had arrived from the north in search of land. Guided by their god Huitzilopochtli, whose figure they carried wherever they went, they had arrived in central Mexico around 1111. For the next 200 years they tried to find a place to stay, offering their services as mercenaries for others but never welcome anywhere.
In 1325 the Aztecs retreated to two small islands in Lake Texcoco and founded Tenochtitlán. Over the next 200 years they extended the city into the lake and connected it to the lake shore with causeways. When the Spanish arrived in 1519 their leader Hernán Cortés considered Tenochtitlán "one of the most beautiful cities of the world." The city, its suburbs and associated coastal settlements had a population of 400,000, the largest and densest concentration of people in Meso-American history.
Through ruthless warfare and open threats the Aztecs established themselves under their leader Montezuma I as the ruling elite over many city states and imposed their religion on them. When Montezuma II became ruler less than 50 years later he inherited an empire that stretched from today's Honduras to Nicaragua.
In the span of a few generations the Aztecs had developed from a nomadic warrior society into one of the most sophisticated civilizations. They remained the most feared military force of the continent, but they also adopted many of the achievements of the neighbouring civilizations. Their cities displayed buildings of great architecture, and the skills of their goldsmiths and silversmiths became legend.
When the Spanish finally took Tenochtitlán in 1520 they melted most of the gold and silver artworks into bullion. The one fifth of the booty they had to give the Spanish king Charles V still filled entire ships. The king inspected only the first load and ordered all arrivals to be melted into bullion to finance his wars in Europe.
The other great civilization in Meso-America was the Maya civilization of the Yucatan Peninsula of Mexico, Guatemala and Belize. By far the longest lasting of all Meso-American civilizations, it arose shortly after 100 AD, disappeared as a political force between 600 and 900, was rejuvenated through migration from Mexico shortly before 1000 and remained the most advanced American civilization until its destruction from the Spanish invaders in the 16th century.
Archaeologists and historians distinguish the Old Empire (320 - 987) and the New Empire that lasted until the Spanish occupation; but that does not imply the existence of a unified political power. For most of its 1500 years the Maya civilization consisted of many city states, comparable to the situation in early Mesopotamia (Sumer) or ancient Greece.
Rivet (1960) lists more than sixty cities for the Old Empire. For reasons still not known they were all eventually abandoned after flourishing for hundreds of years. Some ten new cities were built during the New Empire, which arose after new people migrated from Mexico, adopted Maya language and culture and established political power again and with it the social infrastructure and services.
Chichén Itzá, a city of the Old Empire established in 455 and abandoned in 692, was the only city to be reoccupied in 987. In 1441 its inhabitants left the city to the advancing Spanish forces and retreated to the remote city of Tayasal in Lake Petén that had been abandoned for 600 years, where they could resist the European onslaught for another 200 years. Tayasal fell on 13 March 1697, 205 years after Columbus first set foot on American soil.
Maya society was built on five classes (nobles, priests, commoners, slaves and merchants), a high division of labour and an extensive market system. Cocoa beans were the general currency. Public services were financed through the raising of taxes. During the periods when a true Mayan empire existed it was built on the dominance of one city, which extracted taxes, troops and labour from other cities. Because American civilizations did not know the wheel and Meso-America lacked animals suitable for the transport of goods (the horse arrived in America with the Spanish), the economy was built on local self-sufficiency, long-distance trade being used only for luxury goods.
Having evolved over a period of 1400 years, the Maya civilization was well on its way to develop a true science and was the most advanced of all pre-Columbian civilizations in that respect. Like the Olmecs, Zapotecs and Mixtecs, the Mayans knew how to make paper and had a pictorial script (often referred to as Mayan hieroglyphs). This allowed the Mayas to record all knowledge on long strips of paper, which they folded harmonica-style into books.
The Catholic priests who took part in the Spanish invasion could not read Mayan script. They declared all literature of the Mayas "pagan" and burnt their books in great piles, so that today only three Mayan books are known and kept as treasures in museums. Most of our knowledge of Mayan script comes from stone monuments, and about one third of the pictorial characters have yet to be deciphered.
The Dresden Codex, one of the three rescued Mayan books, is believed to have been produced in the 10th century. It contains predictions of solar eclipses for centuries and a table of predicted positions of Venus and bears testimony to the advanced stage of Mayan astronomy. Mayan cities had observatories with attached libraries. The lack of astronomical instruments was overcome by aligning stars with two objects that were separated by a large distance, a technique that achieved great accuracy of angular measurement. As a result the Mayas developed the most accurate calendar ever designed (see Lecture 7).
The intellectual and scientific centre of the Maya empire was Copán in the extreme south; cultural historians compared it with Athens and Alexandria. Copán's buildings and public places are covered with pictographs, many still awaiting deciphering. Palenque, a city in the north-west of the empire, was its spiritual centre.
There is no doubt that Mayan science was still closely related to religion, similar to science in ancient Egypt or in Greece before 600 BC. Thompson (1954) observed a change in Mayan building activity from religious to mainly secular architecture around 650 AD. Strangely enough he took this as a sign of decline for the Maya civilization. But as we have seen in several other civilizations, they all reach the point where science separates from religion, and it is not at all clear why a declining influence of religion has to be seen as an indicator for the decline of civilization. Whether Mayan science made the step from being a branch of religion to becoming an independent activity around 650 AD remains to be established. Maybe the pictorials of Copán and Palenque hold the key.
The greatest scientific achievement of the Mayas, the position-value number system with zero (discussed in detail in Lecture 5), was a very early development. Date inscriptions found in Monte Albán indicate that it goes back to a number system already used by the Zapotecs. It was adapted for use with the calendar that regulated all life in Mayan society.
A particular trait of all pre-Columbian societies was the concept of quantized time. Most people of our times and earlier European and Asian civilizations see time as continuously flowing and consider the division into hours, minutes and seconds as a convenient but artificial division for the purpose of time measurement. For the Mayas time was divided into days, which represented individual units of time. Each day was carried by the day's god, who picked his burden up at sunrise and set it down at sunset, when time died, to be reborn again the next morning, carried by a different god. There were 20 day gods in all, 20 days making up one uinal (month).
The Mayan concept of time had strong religious connotations. The rebirth of time required daily offerings of food and animal sacrifice and regular human sacrifice at larger intervals. It is a difficult concept to grasp for us today. Some appreciation of the idea of quantized time may be gained when we consider the idea of quantized space.
The idea that the physical world is made up of atoms was proposed by Indian philosopher-scientists (lecture 14) and by some of the early Greek philosophers (lecture 8). Today we have come to accept the idea that solids, fluids and gases consist of particles (such as electrons, neutrons, positrons and others), even though we do not see rocks and water as an ensemble of particles but as objects that occupy a defined part of continuous space.
The issue will concern us again in some detail when we come to a discussion of modern physics in later lectures. Suffice it to say in this context that the dichotomy between continuum physics and particle physics ranks among the major issues of modern science and that the concept of quantized time is now discussed at conferences as a way to arrive at a unified description of the space-time continuum. Maybe future generations will accept the idea of quantized time in the same way as we accept the idea of quantized space.
Aztec books did not suffer the same fate as the Mayan literature, and the so-called Aztec Codices contain much information about Aztec intellectual life. When the Aztecs began to build their civilization they were nomads who had invaded an existing urban society. Two hundred years later the Spanish destroyed what they had built. We may thus compare Aztec civilization at the time of the Spanish conquest with the state of Arab civilization around 850, two hundred years after the beginning of Arab expansion. At that point in time the Arabs had more or less completed the assimilation of the existing science, and mathematicians like al-Khwarizmi were adding new original contributions to the world of science (Lecture 16).
The Aztecs followed the same road. They kept their own script and languages but assimilated all they could learn from Mayan society. Their manuscripts describe how the Mayas performed their astronomical observations. A report on Nezahualpilli, ruler of Tenochtitlán from 1472 to 1515, says about him:
The Aztec state provided formal education to all. Children of noble families attended the calmeacs, schools dedicated to the teaching of skills required for administrators. All children - males and females, commoners and nobles - attended the cuicacalli when they were of age 12 - 15. At these public evening schools "nothing was taught there to youths and maidens but singing, dancing and the playing of musical instruments." (Durán, 1971) This early description of the cuicacalli is certainly misleading, as the content of the songs taught included all aspects of Aztec intellectual tradition from religious tales to the investigation of nature - it is tempting to draw the parallel to the medreses of the Arab world, with the notable difference that in Aztec society girls received the same education as boys.
A discussion of pre-Columbian medicine was part of Lecture 9 and does not have to be repeated here. As in other early civilizations medical treatment consisted of a combination of applied medical knowledge (mainly the knowledge of herbal medicine) and religious incantations and was usually given by priests.
Several outstanding achievements can be reported in the area of technology and invention. The manufacture of rubber was one of the earliest inventions, documented by the use of a rubber ball in the ball game tlachtli, a game played by Meso-American civilizations from earliest times. In architecture the Mayas were the first to use pitched ceilings in their buildings after the invention of the corbelled vault. Aztec city builders also understood the need for public sanitation; public latrines were found along all highways, and to prevent pollution of Lake Texcoco canoes transported the sewage from Tenochtitlán to the mainland every morning. (von Hagen, 1957)
American people were gifted horticulturalists and cultivated crop plants from the earliest times. Among the plants that originated in Meso-America are corn (maize), papaya, avocado and cocoa. Maize is the only cultivated plant that was developed so early in human history that its wild ancestor is no longer known. It can, however, still be crossed with two other plants found only on the Yucatan Peninsula.
Finally, several sculptures found at Meso-American sites in 1975, 1979 and 1983 and dating back to 2000 - 1500 BC have clear magnetic properties. In some of these sculptures the north and south poles are in most conspicuous positions, for example at the snout and at the back of the head of a frog or turtle. Another magnetic object found in 1966 was shaped as if it was to be used to indicate direction. These finds strongly suggest that the early Meso-American civilizations knew about and used magnetism. (Malmström, 1976, 1979)
If one thinks of large rivers as the cradle of civilizations (the Nile, the Indus, the Euphrates and Tigris), the obvious location in South America would be the Amazon. But the rainforests of the Amazon and its tributaries are so tropical that there is little need for irrigation-based agriculture. While recent archaeological research (Heckenberger et al., 2003) uncovered complex regional settlement patterns with large central plazas, wide curbed roads and patches of cultivated or otherwise altered land dated to 1200 - 1600 in the Brazilian Amazon region, there was little need for an administration to look after public works, and the Amazon settlement pattern cannot be called a civilization.
Very different conditions were found on the west coast of South America. The Pacific Ocean offers excellent fishing because of coastal upwelling, but the coastal plains are deserts, and the high elevation of the Andes poses a serious challenge for agriculture and husbandry. The region falls into three ecological zones:
None of these zones could support human sedentary survival on its own, and the Andean people therefore developed societies that stretched over all three zones from the coast to the highest mountains. Between the ecological zones the settled regions of a particular society were separated by several days of travel.
The three zones were shared between different societies, and a traveller on the way from the mountains to the sea would have come through villages belonging to different political centres and possibly end up in a fishing township with suburbs of fisher families speaking different languages and belonging to different political units. Archaeologists call this interwoven pattern of different political units the "Andean ecological complementarity" or "vertical archipelago."
One technological development that occurred very early in these societies was the preservation of food into ch'arki (known in modern English as "jerky"). The method owes its success to a peculiarity of the climate in the tropical high Andes, where daytime temperatures are typical for the tropics but nighttime temperatures are determined by the high elevation and fall below freezing point during 300 days of the year. Meat and tubers frozen during the night remain frozen while the water content evaporates during the day. The conservation method is essentially the same as modern freeze-drying; it prevents food deterioration during the conservation process and allows storage for extensive periods.
From the establishment of Caral before 2600 BC until the establishment of the Inca empire from 1400 AD onward most people of the Andes lived in small mini-states. These states had their administrative centres in fertile river valleys of the high country, where they established irrigation systems. The first major political power arose about 1000 BC with the state of Chavín de Huántar in central Peru. It declined and was followed by the Nazca, Moche, Pucará and Tiahuanaco civilizations, which all flourished from 400 BC.
The Huari civilization, which developed from 600 AD onward and reached its peak development in 800, inherited much from Tiahuanaco. Its city buildings showed the existence of a ruling class and a developed religious organization with a class of priests, a social structure that certainly existed well before, as the big ceremonial centres such as Tiahuanaco indicate. Regrettably these civilizations did not develop a script, so nothing is known of their intellectual and scientific achievements.
The development of bronze in the region of today's Argentina and its introduction into the Andean civilizations accelerated the division of labour and promoted development on a larger scale. The Chimú state, which had its capital Chan Chan in the Moche valley and reached its peak around 1370, redirected entire rivers to expand its irrigation network.
The parallel Chincha state in the south developed seaworthy rafts with keels and sails, and its fishermen travelled to distant fishing grounds along the coast and in the deep sea. The first Spanish to enter Peru were told that the Chincha ruler had a fleet of 100,000 rafts on the ocean. Even if allowance is made for vast exaggeration - a fleet of 1,000 rafts would still signify a significant economical operation based on an important technological achievement.
The size of these dominant states was still small in comparison with Tawantinsuyu, the empire of the Incas that arose only a few decades before the European invasion. When the Spanish arrived the Chincha state had already become part of the Inca empire, and the Inca books listed it as having 30,000 households. When Charles V complained that not a single piece of the newly conquered lands had been given to him as his personal fief, the conquistador Francisco Pissaro gave him the Chinchas. The king did not gain much from his new subjects; no Chincha survived the next thirty years.
Tawantinsuyu, the Inca empire, developed into one of the greatest civilizations of the world. Before its destruction by the Spanish it extended over some 3,800 km from Ecuador to Santiago de Chile and covered parts of today's Ecuador, Peru, Bolivia, Chile and Argentina. From his fortress Sacsayhuaman in the capital Cuzco the Inca emperor ruled over about 20 million people who spoke at least 20 different languages. (Two of these languages, Quechua and Aymara, are still the primary and often the only language of more than 10 million people of Peru, Bolivia and Chile today.)
Before about 1430 the Incas extracted tribute from others through raids. Beginning with emperor Pachacuti they established permanent garrisons and administrative centres in all areas under their control and promoted a new religion that justified their dominance. They expanded the roads inherited from the Chincha into a road system of more than 23,000 km. As the American civilizations did not know the wheel, the roads were constructed for pack animals and pedestrians and provided a rapid communication system between the capital city and all parts of the empire. A system of staged runners guaranteed that messages and orders were transmitted at great speed; the distance between Cuzco and Quito at the northern end of the empire was covered in less than five days, a speed that the European civilization could not match until more than four centuries later (von Hagen, 1977).
It is difficult to assess the development of science in Inca society, but all indications are that compared with the Aztecs the Incas still had a long way to go. There was no script, and all book-keeping was done by placing knots in textile strings known as quipu. There are other textiles with patterned structures and symbols; if they carry messages they have yet to be deciphered.
The character of Inca religion would also suggest that rational understanding of nature had not advanced much. Divination, mostly by inspection of a llama's liver, was a prerequisite for every action. Failure by an individual to observe the strict ritual was believed to inflict harm on the community and required confession and penitence. Animal and human sacrifice was common and not restricted to times of distress. The emperor's poncho (coat) was burnt as a sacrifice to the sun each morning, and every month the priest in Cuzco sacrificed 100 llamas to appease the sun.
Though the Incas could not compete with the Mayas in science, their technology was ahead of every other American society and allowed them to achieve the same high standard of communal living as the Aztec empire through a totally different model. Inca society did not know taxes or markets. Support for the common good took the form of regular annual work for the state. Labour service (mit'a) could take various forms, from road construction to bridge maintenance, work on the state's maize (corn) estates and textile production.
Maize was not the only product produced by the estates. According to van Hagen (1957) more than half of today's food plants originated from the Andes: over 40 varieties of potatoes, several varieties of maize, sweet potatoes, squash, dozens of bean varieties, manioc (the source of farina and tapioca), peanuts, cashews, pineapples, tomatoes, pepper, strawberries, mulberries and many others were first cultivated by the people of the Andes. Among the medicinal drugs quinine, cocaine, ipecac, belladonna and tobacco were first cultivated in the region.
The produced goods were stored in thousands of warehouses; the largest maize estate alone had 2,000 of them. Warehouses were distributed throughout the empire, and warehouses with accommodation were found on all highways, spaced according to one day's travel at llama speed.
In return for mit'a every Inca was entitled to goods from the state's stores. This included food not available locally (preserved as ch'arki) and textiles of various kinds.
The character of Inca society found its legal expression in heavy punishment for offences against the public good. Theft, for example, was regarded as an aberration that could only occur as a result of greed or want. If the theft was committed out of greed the thief received severe punishment; if it was committed out of want the punishment was meted out to the state official who through inept administration had allowed a situation to develop that led to the theft. (von Hagen, 1957)
This system of what could be called state communism required extensive and good book keeping, and the state administration had thousands of quipu in its inventory buildings, where trained accountants kept track of the content of all warehouses. After the arrival of the Spanish the inventory included goods received from the foreigners, goods given in return and even goods stolen by the Spanish. The inventory continued to the very last day of the empire, a grim documentation of its destruction by the European invaders.
The warehouse system contributed much to the downfall of the Inca empire. Wherever they went the Spanish soldiers found stores full of more food than they could ever eat and textiles in large quantities.
The major cause for the empire's downfall, however, was internal strife. The empire had barely been 100 years old when the Spanish arrived; it had just entered its phase of consolidation, and many ethnic groups still bore grudges against the ruling Incas. Conflict in the emperor's family about the succession added to the instability, and at the time of the Spanish arrival the empire was in the midst of a civil war. Many ethnic groups retreated into the high mountains and built or reinforced strongholds such as Machu Picchu to escape the slaughter.
Don Francisco Cusichaq, ruler of the Huanca in central Peru, aligned himself with the Spanish to fight the Incas. It did not do the Huanca any good; they did not fare better under the invaders than any other ethnic group, and Cusichaq bitterly regretted his decision.
Before we come to the end of this lecture and return to the state of science in Europe we spend a few paragraphs on the societies of the South Pacific, a region that experienced European colonization more than 200 years after the destruction of the American civilizations.
The geography of the Pacific islands does not favour the development of civilizations. Of all the islands scattered over a vast area, only Hawaii, Aotearoa (later named "New Zealand" by the European arrivals) and Papua are big enough to support populations of a size that could possibly sustain a major city.
Even on those islands there was little need for a highly developed division of labour and large-scale public works such as irrigation systems. Most islands find themselves in a climate that made provisioning for the daily needs of its people easy. The soil is fertile, the rain plenty, and garden cultivation was more a matter of preventing unwanted plants from growing and taking over than a matter of nurturing a planted crop. The ocean provided an unlimited supply of fish.
The lack of a major civilization in the South Pacific is therefore not the result of any racial predispositioning of its people, and the absence of science in today's sense of the world does not indicate intellectual inferiority. We have to remember that science develops in response to social needs. If you do not have to maintain and operate an irrigation system you do not need a calendar, hence you do not have to develop astronomy. Counting the number of plants in your garden or the number of fish in your daily catch does not require a position-value number system. The people of the South Pacific of today acquire scientific knowledge in response to new social needs that are the result of contact with the outside world, and where these needs occur they are as competent and skilled as anyone.
Evidence for a society that showed the characteristics of an evolving civilization has been found on the island of Pohnpei (Ponape) in Micronesia. The city of Nan Madol was built on platforms that were raised above high tide level and carried houses for some 1,000 people. Its history and area of influence over other Micronesian islands remains to be discovered.
Even a city like Nan Madol would not have required a level of administration and book keeping to stimulate the invention of script. What kind of scientific observations could the islanders have pursued without a script and a developed number system?
The one important skill that required careful and detailed observations was navigation. We know that the various island groups of the South Pacific had regular contact and that islanders regularly visited remote uninhabited islands to harvest their gardens. Given the size of these islands, reaching them in an outrigger canoe requires high navigational accuracy.
The islanders used a combination of techniques to achieve this accuracy. On the open sea they navigated by the stars, but in quite a different way from the way in which the Chinese, Arab and European navigators used astronomical navigation. Without written records they had to rely on oral conservation of knowledge.
For each inter-island route a navigator had to learn and remember the steering stars and follow them during the night. During the day the direction of swell coming from distant regions and the direction of the wind helped to keep the right course. Final landfall was made with the help of additional information, such as clouds generated over islands, the flight of birds of those species that return to roost on islands every night, and changes in the swell pattern produces by reflection and diffraction at the target island.
The South Pacific system of on-the-job training of navigators, combined with theoretical instruction by arranging stones in the sand to represent islands, stars and swell directions, guaranteed the safety of the sea-going parties. Everyone could go out on a canoe and catch fish, but travelling to distant islands required a navigator. Navigation was a highly skilled profession that was passed on to the brightest young people.
Islanders recount stories of navigators who were blown off-course for days by a storm and never thought himself lost. When the storm abated they headed towards the next island and arrived safely. Before the introduction of the chronometer any European or Asian navigator would have been at a loss how to determine position after drifting for days. South Pacific navigators combine their knowledge of the regional swell systems, bird behaviour, estimates of ship drift and star positions to derive an estimate of their position accurate enough to enable them to make landfall even after extensive time at sea.
Lewis (1972) demonstrated the effectiveness of South Pacific navigation by taking a sailing catamaran from Tahiti to New Zealand without compass and sextant. His experiment lead to a revival of the science of South Pacific navigation, and new navigators are trained again in the schools of Micronesia.
South Pacific science is remarkable because it developed and was practiced without a script and without mathematics, yet it had all the characteristics of true science: It was based on verifiable observation, its success was proven through regular application of its predictions, and it did not contain the slightest element of religion or superstition.
Durán, D. (1971) "Book of the Gods and Rites" and "The Ancient Calendar", translated by F. Horcasitas and D. Heyden. University of Oklahoma Press, Norman. (Original dates 1570 and 1579)
Heckenberger, M. J., A. Kuikuro, U. T. Kuikuro, J. C. Russell, M. Schmidt, C. Fausto and B. Franchetto (2003) Amazonia 1492: Pristine forest or cultural parkland? Science 301, 1710 - 1714.
León-Portilla (1969) Pre-Columbian Literatures of Mexico University of Oklahoma Press, Norman.
Lewis, D. (1972) We, the Navigators. Australian National University Press, Canberra.
Malmström, V. H. (1976) Knowledge of magnetism in pre-Columbian Mesoamerica. Nature259 (5542), 390 - 391.
Malmström, V. H. and P. E. Dunn (1979) Pre-Columbian magnetic sculptures in western Guatemala. Time Magazine 3 September 1979.
Rivet, P. (1960) Maya Cities. Translated from the French by M. and L. Kochan. Paul Elek, London.
Thompson, J. E. S. (1954) The Rise and Fall of Maya Covilization University of Oklahoma Press, Norman.
von Hagen, V. W. (1957) The Ancient Sun Kingdoms of the Americas. The World Publishing Company, Cleveland & New York.
von Hagen, V. W. (1977) La Carretera del Sol. Editorial Diana, México.
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