The Haab calendar is very similar to the Gregorian calendar that we use today. It's based on the cycle of the sun and was used for agricultural, economic and accounting activities. Much like the Tzolk'in calendar, it's also comprised of uinals (periods of 20 days), and each day has its own hieroglyph and number. However, instead of using 13 uinals for 260 days, the Haab calendar has 18 uinals, giving it 360 days.
Mayan astronomers noticed that 360 days wasn't enough time for the sun to make it through a full solar cycle. They argued that the calendar should follow the cycle as closely as possible for accuracy. But Mayan mathematicians disagreed. They wanted to keep things simple, in increments of 20, just like their math system. The astronomers and mathematicians finally agreed on the 18 uinals, with five "nameless days" called the wayeb [source: The Maya Calendar].
The wayeb, or uayeb, is considered one "month" of five days thought to be a very dangerous time. The Mayans believed the gods rested during that time, leaving the Earth unprotected. The Mayans performed ceremonies and rituals during the wayeb, hoping that the gods would return once again [source: The Mayan Calendar Portal].
While this calendar was longer than the Tzolk'in, the Mayans wanted to create a calendar that would record even more time. For this reason, the Tzolk'in and Haab calendars were combined to form the Calendar Round.
In the Calendar Round, the 260 days of the Tzolk'in calendar are paired with the 360 days and five nameless days of the Haab calendar. The two calendars are matched the same way the Tzolk'in day names and numbers are (see the illustration of the Tzolk'in calendar on the previous page). This gives the Calendar Round 18,890 unique days, a time period of around 52 years.
At the time, the Calendar Round was the longest calendar in Mesoamerica. Contemporary historians, however, wished to record Mayan history for generations to come. To accomplish that, they needed a calendar that would take them through hundreds, even thousands, of years.
Enter the Long Count calendar.