The katun is the fourth unit of the Maya Long Count, equal to twenty tuns, or 7,200 days, close to twenty years. The ending of a katun was among the most important of Maya calendrical occasions, marked by the erection of carved monuments and by rituals of renewal, and the Yucatec Maya kept a cycle of thirteen katuns, each bearing prophecies, that gave the passage of these periods a prophetic character. Within the Long Count the katun sits above the tun and below the baktun, each step multiplying by twenty. A Long Count date names how many baktuns, katuns, tuns, winals, and kins have elapsed since the mythic starting point. These are the features of the Maya Long Count, the linear calendar the Classic Maya used to fix events across centuries on their carved monuments.
A Katun is twenty Tun, 7,200 days, or approximately 19.7 solar years, the fourth place in the Long Count. Katun endings, particularly the ending of a Katun on the day Ahau (the last of the twenty Tzolk'in day names), were occasions of major ritual and monumental commemoration in Classic Maya cities, recorded on stelae erected specifically to mark the event, and the roughly 20-year Katun cycle also underlies the later Yucatec U Kahlay Katunob, or Short Count, a colonial-period 13-Katun cycle used by Yucatec Maya chroniclers such as the authors of the Books of Chilam Balam after the practice of carving full five-place Long Count dates had generally lapsed at the end of the Classic period, around the tenth century CE. A Long Count's third-place digit, the Katun count within a Baktun, runs from 0 to 19 before the Baktun place increments.