The 260-day sacred round is the heart of the Aztec Calendar, the Mayan calendar and nearly every native calendar of Central America. The sacred round is composed of two cycles, one of 20 named days, and one of 13 numbered days, each of which continuously repeats. It takes 260 days for the two cycles to realign on the beginning day of each cycle (260 = 20 x13).
I will use the term "Mayan Calendar" to refer to a composite generic version of the calendar of Central America. The same basic calendar was used with minor variations by the Mayans, Aztecs, Toltecs, Mixtecs, and hundreds of other tribes throughout North and South American for untold generations. There is, however, surprisingly little difference between most versions, considering that it has been used for about 3,000 years.
The fundamental cycle is the 20-day count. Each of the days was named and had an associated picture or glyph. The 20 day glyphs are shown in a circle in the famous Aztec Calendar Stone. This illustration is only of the central part of that calendar. The 20-day cycle begins at the top and goes around counter-clockwise.
The days were said by the Mayans to represent the steps in a person's life (from before birth to after resurrection). Note that the circular arrangement is important because there are several pairs of opposites. For example, the fifth day in the cycle is "Serpent," and directly opposite the serpent is the "Eagle." The eagle/serpent pair was so important to the Aztecs that their capital (now Mexico City) was founded where they saw the eagle with the serpent in its talons (now immortalized on the Mexican flag.)
Some days may represent the day on which a sacred ordinance is performed. For example the day Jaguar represents being "washed clean" and several tribes had baptism ceremonies. Again, note that opposites are across from each other in the circle of days: Jaguar (Baptism) is opposite Lizard, the day when evil enters a child's life. The symbolic meanings of each glyph is worth knowing, so I explain them in as much detail as I can.