The calendar of the Toltecs, Aztecs and Incas. Before its discovery and domination by the Europeans, America was home to peoples who developed a remarkable civilisation. The most famous of these were the Toltecs who founded a powerful empire around the 7th century in the country now occupied by Mexico and its surrounding area; the Aztecs, initially a barbarous tribe from the North who destroyed the Toltec Empire in the 11th century, inheriting the civilisation of the people it supplanted; and, in South America, the Incas whose empire stretched from the shores of the Pacific to the Andes Cordillera, in an area today encompassed within Peru and Chile. Equally worthy of mention are the Maya and Nahuas, in Yucatan and Central America, and the Chibchas who inhabited the basin of the Magdalena River in today's Colombia. Long before the Christian era and the Spanish conquest, these peoples were familiar with the solar year, the use of the gnomon, the rotation of Mars and Venus, and the appearance of the Pleiades. In the fields surrounding Tlathuica, near Cuernavaca, lie the remains of Xochicalco (place of flowers), at the centre of which stands a famous pyramid, the base of which is decorated with bas-reliefs depicting historical events, each dated according to the calendar of that age. A monolithic stone containing the Aztec calendar was mounted for many years at the base of one of Mexico Cathedral's towers. This stone has since been transferred to the city's National Museum. As with all other peoples, the Toltecs, Maya and Nahuas initially relied on lunar calendars before settling on a 365-day solar year more than three centuries before our era. They even recognized, or learnt from other peoples, that the year was too short because, in 249 BC, the priests and astronomers gathering at Huchuctlapallan decided to add an additional day every four years. They would not have been unaware even that this intercalary day was not enough to bring the calendar year fully in line with the solar year. The Maya and Nahuas began the New Year at the winter solstice, which they recognised from the gnomon as the time when the shadow cast by the sun ceased to increase. Of the 365 days of the year, 360 were divided into 18 months of 20 days each, hence the names given by the Aztecs: 1. Atlcahualco 2. Tlacaxipehualitzi 3. Tozoztontli 4. Huey Tozoztli 5. Toxcatl 6. Etzalcualiztli 7. Tecuilhuitontli 8. Huey Tecuilhuitl 9. Tlaxochimaco 10. Xocotl Huetzi 11. Ochpaniztli 12. Teotleco 13. Tepeilhuit 14. Quecholli 15. Panquetzaliztli 16. Atemozli 17. Tititl 18. Izcalli These 18 months of 20 days gave 360 days to which 5 more days were added at the end of the first month, and a sixth day every four years. Mexico's ancestors used four names to refer to the 20 days of the month: acalt, tecpatl, calli and tocltli, to recall the four winds, the four elements, the four seasons and also the Sun, Venus Moon and Earth. They would repeat these four words in the same order five times in succession in the 20-day month. And although there were originally only these four names, the months consisted of periods of not four but five days, the fifth being a market day. Later on, each of the 20 days had its own individual name: (In Toltec and in English)1. Acalt (Reed) 2. Ocelotl (Tiger) 3. Cuauhtli (Eagle) 4. Cozcauauhtli (Crow) 5. Ollin (Sun) 6. Tecpatl (Arrow or Flint) 7. Quiauitl (Rain) 8. Xochitl (flower) 9. Cipactli (Fish) 10. Ehecatl (wind) 11. Calli (House) 12. Cuetzpalin (Lizard) 13. Coatl (Grass Snake) 14. Miquiztli (Death) 15. Mazatl (Deer) 16. Tochtli (Rabbit) 17. Atl (Water) 18. Itzcuintl (Dog) 19. Ozomatli (Monkey) 20. Malinalli (Dry Grass) The four original words were kept to refer to the 1st, 6th, 11th and 16th days. Before these names were set down in written form, they were represented by symbols reminiscent of Egyptian hieroglyphs or the Chaldaean catasterismi of the zodiac. Thus, the first day, Acalt, which means reed, was depicted by a reed before being written as a word; the 16th by a rabbit's head and the others by an eagle, a flower, a lizard, and so forth. It is in this primitive form that the ancient monuments express the 20 days of the month. The names cited above are those of the Nahua calendar. The Aztec calendar used the same words, or rather the same signs, arranged in a different order. The reed, for example, instead of being the first day, was the thirteenth. The 18 months were also represented by symbols engraved side by side, from the 1st to the 18th, in circular form. In addition, the Toltecs, Maya and Nahuas had a period of 52 years and another of 1,040 years. The Aztecs called the 52-year cycle Xiuhmolpilli, which means "year bundle". It was depicted as a circle at the centre of which was the image of the sun, and around the sun a snake which folded to make four small loops at the four cardinal points of the circle. Each section comprised between two loops was equivalent to one quarter of the circumference and represented 13 years of the cycle. The 52 years were represented by the four primitive symbols referred to above: Acalt (Reed), Tecpatl (Arrow), Calli (House) and Tochtli (Rabbit). These four figures are repeated 13 times in the same order. These peoples then developed the concept of four seasons separated by the four equinox points which they represented using the ends of a cross called Nahui ollin, a symbol that caused astonishment among the Spaniards during their early conquests. The representation of the days, months and years by symbols suggests a kinship between the astronomical science of the ancient peoples of America and that of the Chinese, Chaldaeans and Egyptians. Like the Egyptians, the Toltecs and the Aztecs used hieroglyphs and did not turn to writing until much later. They were also unfamiliar with the use of numbers, in the absence of which symbolic figures were used to represent their numerical characters. Finally, as in Egypt, pyramid remains have been found in these countries. The peoples of South America were less advanced in calendar science than those of Mexico. The Incas had a lunisolar calendar. The winter solstice, which fell on 21 June for them, was a day of great festivity. They knew about it through the use of gnomons. The Chibchas, early inhabitants of todayís Colombia and a fairly civilised people, had only one lunar year made up of 12 lunar months. After the 17th century, at the time of the conquest of Mexico and Peru by the Spaniards, Brazil by the Portuguese, and the colonisation of North America by the French and the English, the European calendar was adopted by the two Americas.