There is a calendar inverted by the Igbo people. This calendar was invented so as to be aware of days and years. Included in the calendar are four market days namely Eke, Orie, Afor, and Nkwo. These days in the Igbo calendar makes a week. That is to say it has 13 months in a year, 7 weeks in a month, and 4 days in a week plus an extra day at the end of the year, in the last month.
The Igbo calendar is said to have had its root steeped in ritualism and symbolism as many parts of the Igbo calendar are dedicated or named to certain spirits (Igbo: Mmuo) and deities (Igbo: Alusi) in the Igbo mythology.
It is also believed that some of the spirits and deities gave the Igbo people knowledge of time. The market days also correspond to the four cardinal points, North, South, East and West.
In line with the Gregorian calendar, some Igbo communities have tried to adjust the thirteen month calendar to twelve months but this have not been attained (at least for this period).
