Maya priests studied the stars and the seasons, and used several different calendars to measure time, record past events, and make predictions. The Maya used a solar calendar called the Haab, which consisted of 18 months of 20 days each. The five remaining days of the year were considered unlucky. A second calendar, the Tzolkin, functioned as a 260-day sacred almanac. Each date was represented by a number between 1 and 13 and by one of the 20 day names. After 13 days, a new cycle began, with each number paired with a different day name. The birthdays of Maya children were marked using this calendar. The day on which a child was born indicated which god would be a guiding force in the child's life. Today, some parents in Guatemala choose words from this calendar as names for their children.

By combining the Haab and the Tzolkin, the Maya formed the "Calendar Round." This third calendar functioned like two interlocking cog wheels with specific numbers and day names coinciding once every 52 years.

What made the Maya number system unique?
The Maya developed a complex, base-20 number system that made it possible to record all numbers using three symbols, a dot representing the number one, a bar representing the number five, and a shell representing zero . The Maya used this system to record their history and observations. Many examples of Maya numbers, a series of recurring horizontal bars and dots, appear in the Dresden Codex—a Maya book from the eleventh century that turned up in Dresden in 1739.

Place value is important in the Maya number system, as it is in our decimal, or base-10, system. Unlike the decimal system, however, in which we move one position to the left on reaching ten, the Maya moved one position up, in multiples of twenty. With this system, the Maya counted into the millions.

Credits: Aztec Calendar Stone © Kimball Morrison/South American Pictures; Codex Madrid Fragment of the Codex of Madrid. Mayan manuscript. Museo de America, Madrid, Spain. Photo © Scala/Art Resource, New York.

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