The Aztecs made great advances in the sciences, especially in astronomy. One of the major events in Aztec history is the building of the Calendar Stone. For 52 years (from 1427 to 1479), the Aztecs had been laboring to build the Calendar Stone. The Calendar Stone was a massive piece of rock 3 feet thick and 12 feet in diameter. Weighing about 24 metric tons, it contained pictographs for the days and months of the Aztec calendar.
The Aztec calendar was a remarkable demonstration of the advances made by the Aztecs in the science of astronomy. It had 18 months, with each month containing 20 days. Thus, 360 days would constitute one year. The Aztecs, however, had determined that the year contained 365 days. Therefore, they added 5 days called the "Nemontemi", or sacrificial days. These days, when added to the already existing 360, raised the number of days in a year to the astronomically correct number of 365. Keeping in mind that this was 103 years before the Gregorian calendar (used in our world today), it's easy to see the level of sophistication that Aztec science had already reached.
Astronomy was not the only science in which the Aztecs had made great advances. They also had made significant strides in medicine. While many Europeans derided the herbal medicine of the Aztecs as a "heathen" practice, or even worse things, such as witchcraft, the medicinal arts of the Aztecs surpassed those of the best doctors of Europe at the time. Aztec medicine was based on two primary areas: spiritual healing and herbal healing. Many of the illnesses that afflicted the Aztecs were attributed to religious reasons: an angry god, bad birth signs, or something to that effect. Therefore, it was only logical that the first step in treating an illness was always prayer, and sometimes animal sacrifice. In conjunction with tese practices was the use of herbal medicine. Even today, many potent herbal remedies can be found in Central America. The Aztecs knew this power of herbal medicines, and therefore concentrated much of their medical science on finding out what herbs could do. Over the generations, the Aztecs accumulated a rather vast knowledge of the herbs in the world around them, as well as the medical properties of each one. It's important to note that unlike many other cultures, the Aztecs concentrated more on curing the symptoms of a disease than getting at the cause of the disease. The reason for this was again rooted in their religious beliefs: they felt that if a god or goddess wishes to afflict them with an illness, they can do nothing to battle the underlying cause (the deity who afflicted the patient). They considered it perfectly within the scope of being a good Aztec, however, to attempt to relieve the patient's symptoms. Their logic in justifying this decision was something along the lines of "Well, if the gods want this man to suffer, they can make my herbs powerless. So if the medicine works, it means that the gods wish for this patient to be relieved." This logic is what kept the science of medicine from being eliminated by the religious leaders of Aztec society, as it had been restrained for a long time in Europe. This logic, or rather the acceptance of it as sound logic, opened the door for many healers and leeches to help patients and ease their pain, without the fear of retribution from a god. Thus, herbal medicine thrived in the Aztec empire, and consequently grew from generation to generation.
Throughout the ages, many civilizations have come and gone. None are considered great, unless they developed writing of one sort of another. The Aztecs, for their part, had a writing system in which they utilized pictographs. Pictographs are simple pictures used as a form of writing. In the Aztec culture, some pictographs represented whole ideas, and some pictographs represented sounds of syllables. Thus, the Aztecs had a writing system which could rival that of any other civilization, even of the Egyptians and Europeans. With this system, they wrote many codices, on which they recorded data pertinent to the operation of the empire. It is through this writing system that we have found much of what we now know about the Aztec religion and society.